On Friday, December 12, 2014 3:18:31 PM UTC, Andrew Gabriel wrote:
The rise in dirt-cheap CU's is something that's happened mainly
in the last 10 years, so I suspect the proportion of houses with
them has grown dramatically - both new houses and rewires.

And, of course, Part P of the building regulations and the '5 week wonders' with a 'Part P qualification'

Owain