PeterE wrote:
No doubt it will end up like Suffolk or Oxfordshire - any cluster of a few houses will merit a 30 mph limit, even on a wide, high-standard main road, frequently extended some way beyond the last house, and often flanked by lengthy 40 mph buffer zones on totally non built up roads

And of course it will further erode any remaining respect for speed limits even when they are appropriate.
This is exactly what happened in Somerset 2 or 3 years ago. The County Council imposed just the same sort of limits and "buffer zones". The BiB were not consulted - it was a purely political act. On the main road I use most often, the A358 Taunton-Minehead road, there were umpteen changes of speed limit, often extremely close together.
Everyone (except the County Council) saw the stupidity of these new restictions; everyone (except tourists and others not familiar with the road) ignored them; the BiB did not enforce them; the new speed limit signs were constantly defaced with yellow paint (naughty, naughty); our MP ridiculed them in the House of Commons and the local press was full of scathing letters denouncing the Council's latest follly.
In the end the Council relented and common sense prevailed.
Moral - stand up to the b*****s!