She claimed unfair dismissal based on the Equal Treatment Directive 76/207/EC and the Sex Discrimination Act 1975.
However, in September 1994, she had received a raise to £250 and her payslip still showed £250 gross and £186.65 net, which apparently demonstrated tax avoidance.
The employer argued that because Mrs Hall was party to an illegal contract, she was not entitled to bring a claim for unfair dismissal.
The Tribunal held that Mrs Hall could not bring a discrimination claim, because she turned a blind eye to the Inland Revenue being defrauded.
Peter Gibson LJ held that her contract was initially lawful and she did not actively participate in the illegality.
(1998) p. 710 it is said that for the defence to apply it is necessary to show that there was a causal link between the illegality in which the claimant was implicated and the loss of which he is now complaining.