What worries me about the NHS's approach to obesity (and the tone of this thread seems to back that up) is the total lack of understanding, and apparently interest, in the psychology of overeating and the emotional issues around food.
Food, and fat, are not neutral issues, especially not for women. The stigma around overeating and obesity (and some of the language on this thread has been very cruel and unnecessary IMO) fuels shame, which fuels denial, depression, and comfort-eating. That stigma and the emotions it produces is always going to come into play when children are weighed or letters sent out. (We used to have regular weight checks when I was a girl at boarding-school and I remember not eating for a few days beforehand and being thrilled when I was actually told to gain weight!)
People are often overweight because they use food for comfort and pleasure. The unhappier they are the more they will do this. The less confident they are the more they will hide away and rely on eating for pleasure. You can see then how a vicious cycle is created.
We know what causes weight gain from a physical point of view. We now need to do more research into how to support people with the factors that are making them unable to implement the vast quantities of advice and information flying around (we are all being advised to death!).
Denial happens when people can't cope with the implications - when what is being asked of them is just too much even if it might not seem so from the outside.
I would like to see more money being put into providing safe alternatives to the wild spaces and streets that were once a child's birthright - adventure playgrounds for example, more playworkers, facilitating more contact with nature.
I'd also like to see less workplace stress, parents less exhausted and overwhelmed, so that quick food that stimulates the pleasure centres in your brain fast is less appealing. But...dream on...
Remember that it takes a long time without the props of pleasure-stimulating food in order to lose weight, and the rewards of being slim won't be felt for a long time, and people are just trying to get through the day, and get their dcs through the day, and the comfort of fattening food is immediate and readily available. So is the relief of vegging out too long in front of the telly or losing yourself in too many computer games. More wholesome pleasures may not be readily available especially if overweight has made you sluggish or self-conscious.
OP, I am not putting you in this category BTW. I am sure you and your daughter lead a healthy enough lifestyle and it sounds as if even if your daughter is a little overweight - and very likely she isn't - it is something that can be corrected without too much difficulty.
I'd just like to see a bit more depth and sensitivity in tackling this issue generally, that's all. I think it would actually get us somewhere towards real progress instead of what I agree with NorthernLurker is a box-ticking exercise.