Hamish:
If you want to get your stuff tested, you might be able to do a deal if you work in a place where stuff has to be PAT tested, otherwise you can take it to them (almost any professional electrician, phone round and ask...) or get them to come to you but don't expect them to make the journey for free!

I do mine myself. I paid about £250 for a Seaford continuity and insulation tester from RS components. Admittedly that would pay for quite a lot of professional testing, but I felt like indulging my technical interest. You can can also pay thousands for a C&G course for electricians (what the jobsworth at one school we played at was going to do, paid for by his employers of course) but I don't think there's anything in the law/regulations that says who has to do the testing, what qualifications they should have or how it should be done. It's actually quite vague, intentionally because in many cases a big issue is how the equipment is being used.

Anyway, once a year I go though everything that plugs into the mains, and check it. On the power supply for the electric keyboard, I check for insulation between mains and the low voltage output, but don't expect earth continuity; on amplifiers and mixers I test both (it's one button press, does both at once). I also test the cables, and open up the mains plugs that aren't moulded-on and check the wires are in the right places, the screws are tight and the fuse has the correct rating (the first time I did this I found a 5A fuse on a power cable that should have been 13A). And I label everything and print out a certificate listing what was tested and when.

Nobody has ever asked to see the documentation, but I like to know that my stuff is safe.

Leadfingers: yes (if you're still watching...)

Les: Hilary? ...De Witt? Splendid work!

Anahata