Again, this is the UK section of the forum, and things are done quite differently than in the US. It is not true that inspections take place only at the time of sale.
There are some differences in different jurisdictions, but typically insurance companies (or leases) will require electrical inspections by a licensed electrician every 10 years for an owner occupied home, Every five years for a rental, and every three years for a caravan.
There is a specific form which is issued, the EICR (electrical installation condition report).
In addition, under current law it is a criminal offense not to notify the local building council when making electrical alterations in a bathroom. And that can void homeowners insurance as well.
There is variation in this, but this is the UK section of the forum, and DIY is just a different kind of project in the UK than in the US.
I don’t want to hijack the thread, and certainly we want to encourage participation, but as a courtesy to other community members when posting in the UK section of the forum there should be at least some attempt to suggest solutions which would be legal and practical in that region.
Submitted with respect.