In Armstong v Strain  1 TLR 856 at 871 Devlin J said about the necessary knowledge in action for deceit:
A man may be said to know a fact when once he has been told it and pigeon-holed it somewhere in his brain where it is more or less accessible in case of need. In another sense of the word a man knows a fact only when he is fully conscious of it. For an action of deceit there must be knowledge in the narrower sense; and conscious knowledge of falsity must always amount to wickedness and dishonesty. When Judges say, therefore, that wickedness and dishonesty must be present, they are not requiring a new ingredient for the tort of deceit so much as describing the sort of knowledge which is necessary.