Comment 9 by AfraidToDie :

Sheer Reason, perhaps the sheer reason lies in our related histories? Our (US) prudish/religious views on sex originated in Britain. We just took it to a higher and more prudish level. We share the same sexual repressive history and most of us will be scarred for life. We often can blame bad traits on the genetics of our parents, so from the US to Britian I’d like to offer a big sarcastic “thanks mom and dad” :-)

Some of what you say is true however it is a bit more complex than that and the idea that attitudes to morality are heritable is of course silly. For a start I would say that Britain does not have the same religiosity it once had. Church attendance is down to 20% and even those who do attend church would often not regard sex outside marriage as 'sinful'. So in the UK the problem is most definitely not down to prudery. We also have free open access to contraception and the morning after pill so there is no reason for these high numbers. I would probably say that the problem lies with education as a lot of our young people do not bother to use contraception as numerous studies have shown a complete ignorance of reproductive issues among a certain demographic.