The dangers of childhood obesity are well known so this is bad news both in absolute terms and relative to the rest of the country.
How have we got here?
No one can claim to have the definitive, scientifically based answer to this but I suspect that there are a number of contributory factors. The cost of living in London means that parents often have to work long hours and schools have not prioritised sport and physical activity as highly as they once did. I'm going to sound like an old grump, but computer/video games have taken over as the primary youth leisure activity for a huge proportion of children.
My supposition is backed up by the report's authors, Liz Cavan (from the CSP) said the children were getting fatter because of “the growth of sedentary leisure activities, the car culture, time and financial constraints on busy working parents and our increasing fears about letting young children run around outdoors without adult supervision.”
I found the last part of that quote quite worrying, I fear that in our desire to protect our children from the statistically small risk of predatory paedophiles we are exposing them to a very large risk of heart disease, cancer and diabetes.