Sorry, lost who said it in the thread but I thought it was really interesting, that compared to other slimmer European countries, people in the UK have spend longer hours working and have less time, which led to the culture of fast and convenient food in many ways.
The only country where you get fewer holidays and less time off (statistically) is USA, and it is the only country where even more of the population is overweight than here.
The other really interesting thing is quality of food, what's available. I think it's completely unfair to blame the overweight and obese majority for lack of willpower. The food which is out there, available on the shelves, sabotages you and you are working against your own evolution/hormones, of course you are bound to fail! Even if you don't take activity levels into account (and the heavier you are the less comfortable you'll be with high activity levels anyway, so it's a vicious circle) 50 years ago people just ate what was available and were effortlessly slim or their natural optimal weight.
However, even "normal" food is very different in different countries. When I first came to the UK(from another European country) I thought chickens on the shelves were turkeys. They looked absolutely massive. If I buy not free range chicken breasts(very rarely, but can't afford free range parts) they basically taste of nothing by themselves, and are mushy. Even free range chicken barely has any flavour. When I went back to my country of origin first time in years and had a chicken soup there recently I nearly cried, it was like an explosion of flavour just in the chicken stock. When I moved to the UK and started eating local food and cooking what my English DH liked, I gained 20% of my weight in 9 months, more than I ever gained in a pregnancy before that.
My French friend who moved to the USA completely ballooned in 6 months. Even though she was seeking out familiar foods and eating maybe 50% of what the local ate, she was unrecognisable when she got back, and previously neither I nor her gave our food/weight/ calories a second thought...If you go to a supermarket in UK, more than 80% of stuff on the shelves is either outright junk or something highly processed :( trying to keep the nation slim is like trying to keep the beach dry. Of course the culture of eating on the go and drinking lattes all day long doesn't help, however if you were a healthy human who was raised as nature intended with appetite regulated by the body, you just wouldn't be able to stuff your face all the time or drink lattes, you'd feel sick and naturally stop.
It used to be like breathing, most people self-regulated without even registering, but decades of the wrong cheap foods foisted on the public and the life being set up in the way which realistically doesn't leave much time for cooking from scratch took care of breaking down all natural self-regulation.