Defendant was smoking on a train where it had been banned under delegated legislation but argued that that ban exceeded the powers conferred on the PA that issued the by-law.
HL held the ban as lawful. However it noted that in criminal charges it is a defence to claim that the delegated legislation criminalising the act in question is ultra vires (i.e. unlawful, whether this was on the basis of procedural or substantive review).
Only the clear language of a statute could take away the right of a defendant in criminal proceedings to challenge the lawfulness of a byelaw or administrative decision where his prosecution is premised on its validity.