But Tiggy, your argument surely makes a presumption that coercion exists in any situation where a wife is married to her husband and her husband is present?
S47 states:
'Any presumption of law that an offence committed by a wife in the presence of her husband is committed under the coercion of the husband is hereby abolished, but on a charge against a wife for any offence other than treason or murder it shall be a good defence to prove that the offence was committed in the presence of, and under the coercion of, the husband'.
I still think that it is for the defence to prove the coercion, not just that she is legally married to him and that he was present. However, I will admit that I am neither a judge or a barrister ? 
If the judge has misdirected the jury, you would have thought that legal bods would have picked up on this.