Though the terminology used by judges and writers is by no means
uniform, the term ‘coercion’ is generally reserved for a special defence
that was available at common law only to a wife who committed certain
crimes in the presence of her husband. It was then presumed that she
acted under such coercion as to entitle her to be excused, unless the
prosecution was able to prove that she took the initiative in committing
the offence. The exact extent of the defence at common law is
uncertain. It did not apply to treason or murder; Hale excluded
manslaughter as well and Hawkins ruled out robbery.

Earlier
authorities allowed the defence only in the case of felonies but later
it seems to have been extended to misdemeanors- but excluding
brothel-keeping; ‘for this is an offence touching the domestic economy
or government of the home in which the wife has a principal share’.

Various
theoretical justifications were advanced for this rule- the identity of
husband and wife’s subjection to her husband and her duty to obey him-
but practical reason for its application to felonies was that it saved a
woman from death penalty when her husband was able, but she was not, to
plead benefit to clergy. This reason disappeared in 1692 when benefit
of clergy was extended to women, yet the rule continued and its scope
increased.

In 1925, however the presumption was abolished by the Criminal justice Act 1925.

Any
presumption of law that an offence committed by the wife in 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 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.

At
first sight, it would seem that all parliament has done is to shift the
burden of proof. But there are difficulties about this, for the
question at once arises, proof of what? And it is not very easy to
answer. Coercion at common law was really a fiction applied when the
wife committed a crime in the presence of her husband and there was no
evidence of initiative by the wife. The common law gives little guidance
as to what is required now coercion is a matter of affirmative proof. A
case of procuring a passport by deception, the court said that the wife
must prove on the balance of probabilities that her will was overborne
by the wishes of her husband so that she was forced unwillingly to
participate in the offence. Neither physical force nor the threat of it
is required.