The final paragraph of the appeal case that the police always seem to miss out when this subject is raised. Reads as follows :-
Application for leave to appeal to the House of Lords refused, but point of general public importance certified as follows:
'That the article 'a folding pocket knife' as mentioned in section 139(2) Criminal Justice Act 1988 as being an exemption subject to subsection (3) to the offence made by section 139(1) means a knife that has a blade that folds, whether or not it (the blade) is capable of being opened and locked into an open position and equally capable of being folded once the mechanism had been operated to unlock the blade.'
Taken from the handed down judgement of the Appeal Court.
Do not believe everything your government publishes on the internet.