Robin wrote

There was a suggestion that younger householders are less keen on DIY. Is
this because they can afford not to, or a reflection of increasing
bureaucratic control?

Combined effect of (a) parents who did less DIY than their parents,

I actually did a lot more than mine did. They did quite a bit of DIY
renovation of a house that had been built before they were born,
but I built one from scratch doing almost all the work myself.

(b) less hands-on experience at school,

None of what I did at school was any use for DIY or building the house.

(c) scare stories from the safety lobbies, encouraging (d) the perception
that it's not allowed (eg all the erroenous warnings that anything to do
with gas "must be fitted by a GASAFE fitter" and that "the electrical
connections must be carried out by a qualified electrician"?

Doesn’t effect DIY like painting the place or making some cupboards etc.