At the risk of sounding pessimistic, this just isn't going to work, and there is no easy solution. Even if you doubled the price of alcopops, they're just going to start buying something else. At the end of the day, kids have more than enough pocket money to buy these things, and a bottle of vodka costs the same as a cinema ticket. Upping the price isn't going to effect them when they know they can get hammered for less than a fiver.
The problem is that kids are feeling like they're grown up at an increasingly young age, and want to do things that they consider to be grown up. Now this doesn't mean pipe and slippers, it means behaving like they think 18 yr olds do, so drink, drugs and sex.
All we can do is clamp down on pubs and off licenses selling alcohol to minors, as well as people supllying drink to minors. Of course this risks making it even more taboo, so parents need to educate their children responsibly as well. Drink doesn't need to be demonised.