Series 3 Brake lights not working

My brake lights have stopped working on my '82 series 3 with servo breaks. I have checked the switch and there is no power going to the switch. Is the power feed to this straight from the fuse box or does it go through anything else first?

Goes through the fuse box as far as I recall.

Yep, as said through the fuse box. I think it shares the fuse with indicators or wipers - can't remember which. Just make sure you're testing it with the ignition on. ;-) ....unlike I did

Well I have now sorted it, although I didn't actually find the problem causing the lack of power. I replaced the flasher relay and in doing so must have disturbed something and started getting power back to the switch. I then cleaned all the contacts in the fuse box in case it was one of those at fault. Having done that however the break lights still didn't work so I had to re-adjust the switch. Is this something that slowly wears over time requiring re-adjustment or is that a sign it is on its way out?

See how it goes. Most replacement switches are rubbish. If you need one look out for a genuine NOS ( new old stock) Lucas type. Even the new Lucas ones are poor and the contacts not precise enough to adjust correctly.