I don't think sex education is bad in the UK at all. At every school I've been to we've had whole terms devoted to it in PSHE, etc. I think when teenagers get pregnant they just blame the establishment because it's far easier than to realise the problem is a hell of a lot more complicated than that. I think some of the more likely causes could be the break-down of the family unit and the de-tabooing of sexuality in society in general.
You are also statistically more likely to have children young if your parents did.
Take for example the recent case (I think it was on a BBC documentary) of 3 sisters getting pregnant. They were 12, 14 and 16 years old, all with children. The mother confessed she had allowed, with her full knowledge, the 12-year-old to have sex in her flat. The 16-year-old's baby was actually her FOURTH pregnancy. She had had two miscarriages and one abortion. The mother had the audacity to blame the school for not teaching them enough.
We had a much, much lower teenage pregnancy rate when sex education didn't exist in this country at all. Why didn't it exist? Because sex was a taboo subject. Now I'm not saying we should withdraw all sex education because that's a regression and it could potentially save a lot of girls from falling into a trap of ignorance. I do disagree with all the benefits teenage mothers are given. The reporter in the sisters' case was alarmed to find out that with all the benefit money added together, the sisters were "earning" a lot more than the reporter was. That's not right.
However, it is a very sticky situation as to what an alternative solution could be. If you withdraw benefits the Government will be criticised for its harshness and a lot of kids could grow up in extreme poverty. However, I think teenage mothers should be made to work as soon as their child has finished breast-feeding. This also sounds harsh, but it's better that the mother realise she can't get a comfy ride for years because she has a child.