I spend half my week in London, and half in the North.
My observation is that people are generally slimmer in London. I attribute that to three things: everyday much more self-propelled movement, a younger than average population, social convention.
I stay fairly near the office. Walking to and from work and doing nothing else/going nowhere else easily gets me 30 mins of brisk walking.
What I’ve noticed as I spend more time there is the desire to walk more: so, if I’m going somewhere (meeting/social activity) I’ll consider walking as the first option or design in a longer walk. When I take the tube I stand.
I’m also much more conscious that I’m overweight vs the significant majority of people I work with. When I return to the Northern offices I see many more fat people. As far as I can work out the demographics (class/age/etc.) aren’t materially different.
Because I can’t exercise meaningfully these days, I’m on a long term change to my eating habits. One stone down, two more to go….