True, the amount of people getting sent back to check in after 'attempting' to get through security is ridiculous. Some passengers as you already mentioned, think that cosmetics and allowed, toiletries etc. 'But you didn't tell me I wasn't allowed my lip gloss'. Well the phrase liquid cosmetics includes anything well... liquid! Lol.
I agree BAA security needs to do an awful lot more to ease the security mess at STN but this problem is not helped by the fact passengers think they can get away with taking all these items through.