I'm not from the UK originally, but what really shocked me when I moved her is how people seem to rely on alcohol to have a good time. It's as if without it, the fun is ruined, and indeed, the concept of stopping after a few seems an issue.
It's not really an issue of age. I personally don't agree with drinking before Uni or there about because most of the fact that most kids really struggle with the notion of knowing when to stop before they get so drunk, they don't know what they are doing and put themselves at risk.
I am raising my kids to be confident and comfortable with who they are. We've had discussions about the notion of being able to have a good time without needing the affect of alcohol to chill out. Whether 13 or 31, you really shouldn't have to rely on it to feel relaxed and in a fun mood. Nothing wrong with enjoying a drink of it, the taste in enjoyable, and it is no different to enjoying an ice cold glass of Coke, but when you start to believe that a party is not worth having without drinks, then something is wrong, and very wrong if you that's how you feel at 13.
DD is 17, has been going to parties since she was about 14/15 and never had a sip of alcohol. As she says, she can have a great time without it whilst knowing she remains safe and with a refresh and clear head the next morning. If anything, she's been the good influence on her friends and more of them have gone on deciding not to drink.
Alcohol is a real issue in our society, be it for what it leads people to do, as well as to how it affects our health. Telling a 13 yo that it is ok to have drinks at parties, whether be at home or not, is really not a good example of parenting.