INTRODUCTION
Offences of strict liability are those crimes which do not require mens rea with regard to at least one or more elements of the actus reus. The defendant need not have intended or known about that circumstance or consequence. Liability is said to be strict with regard to that element. For a good example see:
R v Prince[1875]：The defendant ran off with an under-age girl.  He was charged with an offence of taking a girl under the age of 16 out of the possession of her parents contrary to s55 of the Offences Against the Person Act 1861. The defendant knew that the girl was in the custody her father but he believed on reasonable grounds that the girl was aged 18. It was held that knowledge that the girl was under the age of 16 was not required in order to establish the offence.  It was sufficient to show that the defendant intended to take the girl out of the possession of her father.
It is only in extreme and rare cases where no mens rea is required for liability, thereby making the particular offence "absolute".
GENERAL PRINCIPLES
The vast majority of strict liability crimes are statutory offences. However, statutes do not state explicitly that a particular offence is one of strict liability. Where a statute uses terms such as "knowingly" or "recklessly" then the offence being created is one that requires mens rea. Alternatively, it may make it clear that an offence of strict liability is being created. In many cases it will be a matter for the courts to interpret the statute and decide whether mens rea is required or not. What factors are taken into account by the courts when assessing whether or not an offence falls into the category of strict liability offences?
THE MODERN CRITERIA
In Gammon (Hong Kong) Ltd v Attorney-General for Hong Kong [1984], the Privy Council considered the scope and role of strict liability offences in the modern criminal law and their effect upon the "presumption of mens rea". Lord Scarman laid down the criteria upon which a court should decide whether or not it is appropriate to impose strict liability: "In their Lordships' opinion, the law … may be stated in the following propositions … : (1) there is a presumption of law that mens rea is required before a person can be held guilty of a criminal offence; (2) the presumption is particularly strong where the offence is "truly criminal" in character; (3) the presumption applies to statutory offences, and can be displaced only if this is clearly or by necessary implication the effect of the statute; (4) the only situation in which the presumption can be displaced is where the statute is concerned with an issue of social concern, and public safety is such an issue; (5) even where a statute is concerned with such an issue, the presumption of mens rea stands unless it can be shown that the creation of strict liability will be effective to promote the objects of the statute by encouraging greater vigilance to prevent the commission of the prohibited act."
(1) PRESUMPTION OF MENS REA
Courts usually begin with the presumption in favor of mens rea, seeing the well-known statement by Wright J in Sherras v De Rutzen：There is a presumption that mens rea, or evil intention, or knowledge of the wrongfulness of the act, is an essential ingredient in every offence; but that presumption is liable to be displaced either by the words of the statute creating the offence or by the subject-matter with which it deals, and both must be considered
(2) GRAVITY OF PUNISHMENT
As a general rule, the more serious the criminal offence created by statute, the less likely the courts is to view it as an offence of strict liability. See:
Sweet v Parsley [1970]： The defendant was a landlady of a house let to tenants. She retained one room in the house for herself and visited occasionally to collect the rent and letters. While she was absent the police searched the house and found cannabis. The defendant was convicted under s5 of the Dangerous Drugs Act 1965, of "being concerned in the management of premises used for the smoking of cannabis". She appealed alleging that she had no knowledge of the circumstances and indeed could not expect reasonably to have had such knowledge.The House of Lords,quashing her conviction, held that it had to be proved that the defendant had intended the house to be used for drug-taking, since the statute in question created a serious, or "truly criminal" offence, conviction for which would have grave consequences for the defendant. Lord Reid stated that "a stigma still attaches to any person convicted of a truly criminal offence, and the more serious or more disgraceful the offence the greater the stigma". And equally important, "the press in this country are vigilant to expose injustice, and every manifestly unjust conviction made known to the public tends to injure the body politic [people of a nation] by undermining public confidence in the justice of the law and of its administration."
Lord Reid went on to point out that in any event it was impractical to impose absolute liability for an offence of this nature, as those who were responsible for letting properties could not possibly be expected to know everything that their tenants were doing.
(3) WORDING OF THE STATUTE
In determining whether the presumption in favor of mens rea is to be displaced, the courts are required to have reference to the whole statute in which the offence appears. See:
Cundy v Le Cocq (1884) ：The defendant was convicted of unlawfully selling alcohol to an intoxicated person, contrary to s13 of the Licensing Act 1872. On appeal, the defendant contended that he had been unaware of the customer's drunkenness and thus should be acquitted. The Divisional Court interpreted s13 as creating an offence of strict liability since it was itself silent as to mens rea, whereas other offences under the same Act expressly required proof of knowledge on the part of the defendant. It was held that it was not necessary to consider whether the defendant knew, or had means of knowing, or could with ordinary care have detected that the person served was drunk. If he served a drink to a person who was in fact drunk, he was guilty. Stephen J stated:
Here, as I have already pointed out, the object of this part of the Act is to prevent the sale of intoxicating liquor to drunken persons, and it is perfectly natural to carry that out by throwing on the publican the responsibility of determining whether the person supplied comes within that category.
(4) ISSUES OF SOCIAL CONCERN
See :R v Blake (1996) :Investigation officers heard an unlicensed radio station broadcast and traced it to a flat where the defendant was discovered alone standing in front of the record decks, still playing music and wearing a set of headphones. Though the defendant admitted that he knew he was using the equipment, he claimed that he believed he was making demonstration tapes and did not know he was transmitting. The defendant was convicted of using wireless telegraphy equipment without a license, contrary to s1 (1) Wireless Telegraphy Act 1949 and appealed on the basis that the offence required mens rea.
The Court of Appeal held that the offence was an absolute (actually a strict) liability offence. The Court applied Lord Scarman's principles in Gammon and found that, though the presumption in favor of mens rea was strong because the offence carried a sentence of imprisonment and was, therefore, "truly criminal", yet the offence dealt with issues of serious social concern in the interests of public safety (namely, frequent unlicensed broadcasts on frequencies used by emergency services) and the imposition of strict liability encouraged greater vigilance in setting up careful checks to avoid committing the offence.
(5) IS THERE ANY PURPOSE IN IMPOSING STRICT LIABILITY?
The courts will be reluctant to construe a statute as imposing strict liability upon a defendant, where there is evidence to suggest that despite his having taken all reasonable steps, he cannot avoid the commission of an offence. See:
Sherras v De Rutzen [1895]: The defendant was convicted of selling alcohol to a police officer whilst on duty, contrary to s16(2) of the Licensing Act 1872. He had reasonably believed the constable to be off duty as he had removed his arm-band, which was the acknowledged method of signifying off duty. The Divisional Court held that the conviction should be quashed, despite the absence from s16 (2) of any words requiring proof of mens rea as an element of the offence. Wright J expressed the view that the presumption in favor of mens rea would only be displaced by the wording of the statute itself, or its subject matter. In this case the latter factor was significant, in that no amount of reasonable care by the defendant would have prevented the offence from being committed. Wright J stated: "It is plain that if guilty knowledge is not necessary, no care on the part of the publican could save him from a conviction under section 16, subsection (2), since it would be as easy for the constable to deny that he was on duty when asked, or to produce a forged permission from his superior officer, as to remove his armlet before entering the public house. I am, therefore, of opinion that this conviction ought to be quashed."
MODERN EXAMPLES
The following case is a modern example of the imposition of strict liability: Alphacell v Woodward [1972] The defendants were charged with causing polluted matter to enter a river contrary to s2 of the Rivers (Prevention of Pollution) Act 1951. The river had in fact been polluted because a pipe connected to the defendant's factory had been blocked, and the defendants had not been negligent. The House of Lords nevertheless held that the defendants were liable. Lord Salmon stated: If this appeal succeeded and it were held to be the law that no conviction be obtained under the 1951 Act unless the prosecution could discharge the often impossible onus of proving that the pollution was caused intentionally or negligently, a great deal of pollution would go unpunished and undeterred to the relief of many riparian factory owners. As a result, many rivers which are now filthy would become filthier still and many rivers which are now clean would lose their cleanliness. The legislature no doubt recognized that as a matter of public policy this would be most unfortunate. Hence s2(1)(a) which encourages riparian factory owners not only to take reasonable steps to prevent pollution but to do everything possible to ensure that they do not cause it.
ARGUMENTS FOR STRICT LIABILITY
 1. The primary function of the courts is the prevention of forbidden acts. What acts should be regarded as forbidden? Surely only such acts as we can assert ought not to have been done. Some of the judges who upheld the conviction of Prince did so on the ground that men should be deterred from taking girls out of the possession of their parents, whatever the girl's age. This reasoning can hardly be applied to many modern offences of strict liability. We do not wish to deter people from driving cars, being concerned in the management of premises, financing hire purchase transactions or canning peas. These acts, if done with all proper care, are not such acts as the law should seek to prevent.
2. Another argument that is frequently advanced in favor of strict liability is that, without it, many guilty people would escape - that there is neither time nor personnel available to litigate the culpability of each particular infraction. T his argument assumes that it is possible to deal with these cases without deciding whether D had mens rea or not, whether he was negligent or not. Certainly D may be convicted without deciding these questions, but how can he be sentenced? Suppose that a butcher sells some meat which is unfit for human consumption. Clearly the court will deal differently with (i) the butcher who knew that the meat was tainted; (ii) the butcher who did not know, but ought to have known; and (iii) the butcher who did not know and had no means of finding out. Sentence can hardly be imposed without deciding into which category the convicted person falls.
3. The argument which is probably most frequently advanced by the courts for imposing strict liability is that it is necessary to do so in the interests of the public. Now it may be conceded that in many of the instances where strict liability has been imposed, the public does need protection against negligence and, assuming that the threat of punishment can make the potential harm doer more careful, there may be a valid ground for imposing liability for negligence as well as where there is mens rea. This is a plausible argument in favor of strict liability if there were no middle way between mens rea and strict liability - that is liability for negligence - and the judges have generally proceeded on the basis that there is no such middle way. Liability for negligence has rarely been spelled out of a statute except where, as in driving without due care, it is explicitly required. Lord Devlin has said: "It is not easy to find a way of construing a statute apparently expressed in terms of absolute liability so as to produce the requirement of negligence."
ARGUMENTS AGAINST STRICT LIABILITY
 1. The case against strict liability, then, is, first, that it is unnecessary. It results in the conviction of persons who have behaved impeccably and who should not be required to alter their conduct in any way.
2. Secondly, that it is unjust. Even if an absolute discharge can be given D may feel rightly aggrieved at having been formally convicted of an offence for which he bore no responsibility. Moreover, a conviction may have far-reaching consequences outside the courts, so that it is no answer to say that only a nominal penalty is imposed.
3. The imposition of liability for negligence would in fact meet the arguments of most of those who favor strict liability. Such statutes are not meant to punish the vicious will but to put pressure upon the thoughtless and inefficient to do their whole duty in the interest of public health or safety or morals." The "thoughtless and inefficient" are, of course, the negligent. The objection to offences of strict liability is not that these persons are penalized, but that others who are completely innocent are also liable to conviction. Though Lord Devlin was skeptical about the possibility of introducing the criterion of negligence (above), in Reynolds v Austin (1951) he stated that strict liability should only apply when there is something that the defendant can do to promote the observance of the law - which comes close to requiring negligence. If there were something which D could do to prevent the commission of the crime and which he failed to do, he might generally be said to have failed to comply with a duty - perhaps a high duty - of care; and so have been negligent.
4. In Alphacell v Woodward (1972) Lord Salmon thought the relevant statutory section, "encourages riparian factory owners not only to take reasonable steps to prevent pollution but to do everything possible to ensure that they do not cause it." This suggests that, however vast the expenditure involved, and however unreasonable it may be in relation to the risk, D is under a duty to take all possible steps. Yet it may be doubted whether factory owners will in fact do more than is reasonable; and it is questionable whether they ought to be required to do so, at the risk - even though it be unlikely - of imprisonment. The contrary argument is that the existence of strict liability does induce organizations to aim at higher and higher standards.
POSSIBLE DEVELOPMENTS
There are several possible compromises between mens rea and strict liability in regulatory offences. A "halfway house" has developed in Australia. The effect of Australian cases is: D might be convicted without proof of any mens rea by the Crown; but acquitted if he proved on a balance of probabilities that he lacked mens rea and was not negligent; ie, that he had an honest and reasonable belief in a state of facts which, would have made his act innocent. The onus of proving reasonable mistake is on D.
STATUTORY DEFENCES
 It is common for the drastic effect of a statute imposing strict liability to be mitigated by the provision of a statutory defense. It is instructive to consider one example. Various offences relating to the treatment and sale of food are enacted by the first twenty sections of the Food Safety Act 1990. Many, if not all, of these are strict liability offences. Section 21(1), however, provides that it shall be a defense for the person charged with any of the offences to prove that he took all reasonable precautions and exercised all due diligence to avoid the commission of the offence by himself or by a person under his control. Statutory defenses usually impose on the defendant a burden of proving that he had no mens rea and that he took all reasonable precautions and exercised all due diligence to avoid the commission of an offence. The effect of such provisions is that the prosecution need do no more than prove that the accused did the prohibited act and it is then for him to establish, if he can, that he did it innocently. Such provisions are a distinct advance on unmitigated strict liability.