Defences in UK Law

As a matter of public policy, it seems to us essential to limit the defence of duress by means of an objective criterion formulated in terms of reasonableness. In provocation the words or actions of one person break the self-control of another. In duress the words or actions of one person break the will of another. The law requires a defendant to have the self-control reasonably to be expected of the ordinary citizen in his situation.

The Crown having conceded that the issue of duress was open to the appellant and was raised on the evidence, the correct approach on the facts of this case would have been as follows: (1) Was the defendant, or may he have been, impelled to act as he did because, as a result of what he reasonably believed King had said or done, he had good cause to fear that if he did not so act King would kill him or (if this is to be added) cause him serious physical injury?

I would therefore conclude on Issue (1) that the mistake of law rule should no longer be maintained as part of English law, and that English law should now recognise that there is a general right to recover money paid under a mistake, whether of fact or law, subject to the defences available in the law of restitution.

To me, it is plain that the money was indeed paid over under a mistake, the mistake being a mistake of law. The payer believed, when he paid the money, that he was bound in law to pay it. He is now told that, on the law as held to be applicable at the date of the payment, he was not bound to pay it. Plainly, therefore, he paid the money under a mistake of law, and accordingly, subject to any applicable defences, he is entitled to recover it.

Of course, I recognise that the law of restitution must embody specific defences which are concerned to protect the stability of closed transactions. The defence of change of position is one such defence; the defences of compromise, and settlement of an honest claim (the scope of which is a matter of debate), are others. It is based on the theory that a payment made on that basis is not made under a mistake at all.

I would therefore hold that money paid by a citizen to a public authority in the form of taxes or other levies paid pursuant to an ultra vires demand by the authority is prima facie recoverable by the citizen as of right.