And there are still muppets installing CU's without doing any testing :-( Just been to quote for some minor works at a property. 10 months ago I lost out on the board change and some other work. Householder showed me the "certificate".
They have both the top copy and the carbon one. No serial number, no contractor address, no schedule of test results at all. And gems such as "means of earthing : rod by front door. Ra N/A" No PFC, No Ze. Illegible scrawl for design. Illegible scrawl for construction, no signature for I&T. Lost the will to live before I got half way through the schedule of inspections. There's a 16mm T&E sub-main (hopefully) crimped and taped hanging in free air about a foot away from the new board, which has missing blanks and exposed bus-bar.
So yes, B&Q will probably carry on selling their ÂŁ50 specials. It is not their responsibility to ensure the correct installation. In the same way that they can sell bricks, sand and cement which some cowboy can use to build a 6 feet high 1/2 brick retaining wall.
Edit. They were happy with the cert - they had some paperwork so must be OK. Joe Public, even if they know they should have a cert, have no interest, or clue, about what information it should contain.
And their "electrician" is registered with a scheme.