bensonby: I don't see why it is rude to ask for the case reference. I can't find one either relating to Mitchells and Butlers. Perhaps John H can tell us, pretty please.
I found the one that I knew of that ticket (invoice) charges have to be reasonable (i.e. under a £100 or roughly what a local authority can legally charge), which is: https://www.supremecourt.uk/cases/docs/ ... dgment.pdf
Jump to Page 60 of 124 (on my screen) and read "ParkingEye Limited v Beavis - facts", preferably with eyelid matchsticks for another 30+ pages. It's actually very informative about what is considered a "reasonable" charge and why as opposed to a penalty as regards managed car parks who have to be self-funding.
Later, starting at Clause 200 (P.89 on my screen), that deterrent fees and interest charges according to EEC directive are permissible (as not being penalties) if they are of a suitable amount needed to dissuade from not abiding by rules or repaying debts on time.
An aside: I kept wondering why ultra ridiculous loan interest rates and some bank charges aren't usury if unrelated to damage cost. Now I know. They're OK if the raison d'etre is of being a *cough* "reasonable" deterrent.