When I was growing up there were always the odd fat kid in school that people used to take the mickey out of, a kind of peer pressure to slim down and be like the rest of the pack, a herd mentality if you will. With the advent of human rights and political correctness, which is basicly a law to protect freeks and people who deveate from what was intended for us, we can no longer apply this pressure in schools for fear of being called bullies or fattist. Couple this with a surge in lazy parents, advertising for fatty foods, and no competitive sports in schools (its the taking part that counts) no wonder we have a nation of fat useless lazy kids comming through, you could also add stupid to the list because the education system is absolute rubbish. The labour government spent billions in schools on new buildings and teaching kids how to be PC and not to pick on fat kids and completely forgot to teach the kids anything useful. The O level exams used to be hard and although they were a bit easier the GCSE exams taken in the early 90's were alot harder than the ones taken today, download some for yourself.
An initiative to get kids to excersie a bit won't work, competitive sports, healthy eating, banning artificial additives, and kicking lazy parents of fat kids up the backside, even that might not work, but its a start.