The consequence was that in a strike, employees merely "working to rule" needed not to be paid, because they had only partly performed their obligations.

Their industrial action was to comply strictly with the rule book of the British Railways Board.

ASLEF argued that the criteria of the time, that there was ‘irregular industrial action short of a strike’ was not satisfied, because workers had not breached their contracts.

That is plainly the case where a man is employed singly by a single employer… There are many branches of our law when an act which would otherwise be lawful is rendered unlawful by the motive or object with which it is done.Buckley LJ concurred and said it was an implied term to serve the employer faithfully.

Roskill LJ said the implied term was that obedience to lawful instructions should not be carried out so unreasonably that things were disrupted.