Copeland, you described the situation perfectly. My wife inadvertedly left a sculpture tool a few inches long, in her bag, which was found at GRO by security. They told her she was welcome to take it with her but added "you know it will be confiscated at Stansted on the way back". Since it was expensive, the friendly Guardia Civil allowed her to hand it back to me waiting to see her off.
Bags, foodstuffs, liquid etc., all at the discretion of the staff there, who are able to think for themselves, assess the situation, and make their own decisions. The first word of the next sentence would be "Unlike..." but I won't go on as it's from the School of the Bleedingly Obvious, as Basil Fawlty would have said.
New flavour of the Month: TGV from Perpignan to London via Paris. Much nicer !