I agree, this is not a JAR issue.
I don't know about the argument that hire of the aircraft and instructor is all-inclusive. In my experience, most flying schools have posted notices, or provide their students/renters with written policies, that expressly exclude landing fees. If your school didn't do that, you might credibly be able to say that you thought the 200 pounds included everything. But before you go down that road, double-check whatever communications you received from the school to ensure that landing fees weren't mentioned.
MLS-12D
P.S. The scenario posed by EPW actually happened to me when I was doing my night rating. My instructor proposed doing a 'low and over' at Buttonville airport, on the basis that no landing fee would be charged. About two weeks later (surprise!), the flying school received a bill for C$18 (approx., I can't recall exactly), which they added to my account. Needless to say, I wasn't thrilled (particularly when there was no need to do the 'low and over' in the first place), but it was an honest mistake and, like expedite_climb, I let it go. If the bill had been for 10x the amount, I wouldn't have been so forgiving, however!