I have found an acceptable solution to the 1st series brake light switch …..
It is a motorbike side stand switch from a Yamaha Nmax. It fits very neatly and the only issue I found was that it's impossible to fit the upper mounting screw. However it has a solid aluminium case and the bottom one is probably enough with a solid,tight bottom bolt and spring washer.
In order to improve the fit I filed a tiny bit off the edge next to the pedal stop and top edge because it just touched the pedal assembly
Easier to fit with pedals out, but do-able without removing them
I added a cable tie for good measure, but it is pretty much jammed in place as well
I suspect there will be slight variations between cars, so if anyone does try it, please let me know how they get on !
Costs about £30-£40 depending on the source