Concerned I have the smae musings.. but would counter some of them in my mind with the fact that this lack of time and choosing to do other things instead of cook from scratch is a culture thing for the UK rather than a forgone conclusion.
For example "When we look at what little family time we often have, who wants to spend it cooking from scratch, who has time to plan healthy prepared lunches to take with the next day?" A lot of my partner's family are Italian and the women spend a good few hours of an evening making pasta all together, they make and freeze lasagne and have a great time, the children help too (won't get in to what on earth the men are doing during these times!)
I cook from scrtach every night and my DD sits in the kitchen doing her homework and we chat, I would say this is a fun use of time and means we all have a healthy dinner. There will be people who literally DO NOT have the time but as I say, there are people who say they don't have the time, but happily spend 2 hours watching TV. If you want to do that instead of cook that is your choice of course, we all have different priorities.
I eat at my desk but I pack a lunch which is healthy so again, not really a reason to put on weight.
All the slim people I know eat less and when they do eat it is generally healthy food. They don't all take active exercise. In fact most of them don't. But i don't buy in to this "I'm fat because of my genes, I eat like a bird but I put on weight" You only have to look and children in the 3rd world to know this isn't true.
I can't remember the figures but I read somewhere that in the UK we spend the smallest portion of our income on food. The french spend a very high portion.
How many people "can't afford" fresh fruit and vegetables, organic food and good quality wine... but have a cupboards full of DVDs, cigarettes, beers, and eat take aways and go to the cinema & take package holidays etc. I know that sounds naive as there are many people who can't afford any of that, and for them it seems easier to reach for the 2 for 1 value burgers, but I do think over all we don't value good food highly enough as a nation.