Gordon noted that Hume21 and similarly Alison22 expressly rejected a defence of necessity, although he only dealt with it in relation to the traditional plea of Burthensack relative to the capital offence of theft23. Burthensack was a mitigatory defence, which was rejected, for a man who stole as much meat as he could carry on his back due to starvation and therefore necessity.
The reasons behind the rejection included the difficulties in deciding which cases were genuine and which were fake; devising a satisfactory test for necessitous situations and the possible weakening of the law if an accused could break the law, even in restricted circumstances, and not be punished24. The court in Moss v. Howdle25 deliberately ignored Hume and Alison's authoritative writings, but founded on Hume's definition of coercion as discussed in the case of Thomson v.
HMA26 and used that as a foundation for a defence of necessity stating that the two pleas were in principle indistinguishable. This was a judicious, if perhaps questionable, means of circumventing Hume's standpoint, which the courts are reluctant to depart from. There have also been critics in modern times of a defence of necessity being made available, the principal argument taking the same line as Hume in that such a defence may lead to a weakening of the deterrent effect of the criminal law.
Gordon recognises that 'the possibilities of abuse are considerable'28 and it has been suggested that the plea is seen by accused with no genuine defence as a last resort which they may as well aim for29, however if the defence is restricted to the current narrow bounds and not developed significantly in relation to the requirements discussed above, feigners would be very unlikely to succeed.
The Stair Memorial Encyclopedia opines that 'Only an extreme formalist, incapable of seeing beyond the strict letter of the law, could argue against some recognition of necessity'30 and it has been remarked that not to acknowledge such a defence would be 'irrational and unjust'31. These two latter comments are true, it would be ridiculous to punish a man who, for example, drove while disqualified in an effort to take his child, who had fallen out of a tree and hit his head, to hospital when he had no access to a telephone to call an ambulance.
This was the kind of 'choice' the court in Perka referred to when it said it was 'remorselessly compelled by normal human instincts32'. The court in Moss did not comment on any juridical basis for the defence, however in Perka, which they found highly persuasive when identifying the requirements of the defence, the Supreme Court of Canada fully addressed the theoretical thinking behind necessity and discussed alternative approaches.
They recognised that the defence could be seen as either a justification or alternatively an excuse. A justification would withdraw the criminal liability from the act, Gordon observes this utilitarian approach would involve 'weighing up the competing interests in order to assess whether the criminal conduct of the accused was justified as having secured a greater good or lesser evil than the one avoided'33, this approach was thought by the court to introduce subjectivity into the law and therefore was not favoured.
The preferred approach was that of an excuse, which acknowledged the act was wrong, but excused it because there was no real choice but to commit it. The Canadian court stated the excuse principle 'rests on a realistic assessment of human weakness, recognizing that a liberal and humane criminal law cannot hold people to the strict obedience of laws in emergency situations where normal human instincts, whether of self-preservation or of altruism, overwhelmingly impel disobedience'.
This humanitarian attitude goes hand in hand with the principle that only voluntary acts are punishable by law and an accused is acting in effect 'involuntarily' when he commits the criminal offence as it was realistically necessary. It has been suggested that the main reason for Hume rejecting a defence of necessity was that he believed that an accused who had successfully pleaded the defence would be regarded as having been justified in committing the crime and 'laudable as that of a police officer who arrests by force a dangerous criminal who resists the warrant that the officer carries'34.
If the court in Moss had followed the Canadian court in Perka in relation to the excuse principle they could have perhaps addressed Hume's rejection of necessity but got around it by denying that the defence justified the criminal act as he had possibly believed. In England, the courts expressly rejected necessity as a defence to murder in the case of R. v. Dudley and Stephens 35. That case involved the accused being convicted of the murder of a young man whom they had killed and fed on in order to save their own lives.
Gordon states the law in Scotland to be the same as in England in relation to desperate situations where the termination of one man's life could save another man's life. He asserts that a person could never escape criminal responsibility where he kills someone with the aim of saving himself36, (other than in cases of self defence which are not relevant here), matters must be left to take their own course. The defence of necessity should never be made available to an accused in that situation in Scotland, if it was, the law would be made a mockery and ridiculed by society.
Gordon37 notes that 'Professor Glanville Williams suggests, that "We need a general rule, and one allowing necessity as a defence to homicide where the minority are killed to preserve the majority is on the whole more satisfactory than the opposite"'38. This is a very real point following the terrorist attacks on New York on 11th September, 2001 where thousands of lives would have been saved if the aeroplanes had been shot down.
There is no authority in Scotland or England in relation to protection of mass third parties in this way, the circumstances are distinguishable from Dudley and Stephens and it would be unjust to find a person culpable where he had taken, say, 250 lives to save 2,500. The law of necessity should be expanded in this restricted way to take account of modern international troubles. The English case of Re A (Children)39 concerned conjoined twins, Mary and Jodie.
The court used the law of necessity to justify the intentional killing of the weaker twin, Mary in order to save Jodie's life, perhaps this case will be looked to in the future as persuasive authority to expand the law in Scotland. In this kind of situation it would be beneficial to treat necessity as a justification rather than an excuse. In conclusion, Scotland should certainly allow a defence of necessity. It would be unjust and unreasonable not to, indeed in cases such as medical emergency it would be nonsensical.
The requirements as set out in Moss should not be broadened to account for anything less than immediate danger of death or great bodily harm to the accused or a third party. In cases such as road traffic offences and damage to property, necessity should be viewed as an excuse rather than as a justification, it is conceded that this approach does not alter the availability of the defence in any circumstances, but it may encourage acceptance of the defence by those who do not regard it with enthusiasm40.
It has been said that 'necessity creates the law; it supersedes rules; and whatever is reasonable and just in such cases, is likewise legal. 41' In these modern times of terrorism, it would be reasonable and just to extend necessity to situations where a number of people are killed, strictly in circumstances where they would have died anyway, to avoid a much greater number dying.
Busby, N. , et al., Scots Law: A Student Guide, edited by Mays, R. , (Butterworths, 2000) p. 556 Christie, M. , 'The Mother of Invention? Moss v Howdle' 1997 ELR 1(4) 479 Ferguson, P. , 'Necessity and Coercion in Criminal Law' 1997 SLT (News) 127 Ferguson, W. , 'Necessity and Duress in Scots Law'  Crim. L. R. 103 Gane, C. H. W. and Stoddart, C. N. , A Casebook on Scottish Criminal Law, (3rd ed, Edinburgh: W. GREEN/Sweet & Maxwell, 2001) pp. 255-275.