My brother works at Gatwick airport and shortly after the 'Face cream can bring down airliners' story, he related this encounter.

He had to go through security and wanted to take a bottle of (unopened) water. He was prevented by the guard and was told he could buy bottled water inside. He asked why those bottles were safe, to be told that those inside had been 'screened'. He offered to hand his bottle over to be Xrayed, to then be told that they could not detect explosives with xrays. He then asked how they screened the bottles of water inside, to be told that every item goes through the xray machine.

At this point the guard got a bit flustered, possibly from his own logic breakdown, and came up with the typical fallback argument - "those are the rules and if you dont follow them we won't allow you through".