After about 10 minutes driving, my front off-side brake is binding quite badly and heating up the wheel considerably. Steering isn’t affected but throttle response is and takes more gas to leave from a standstill.
When I jacked up and checked for binding (30 minutes after arriving home) there was no binding at all.
Went out for another run and jacked up immediately on arrival home . . . . Brake was binding but after 20 mins or so, was totally “Free”
Any suggestions what is wrong / what I should be checking
All the above plus caliper piston seizing. It depends how good you are with a spanner, i stripped and resealed mine (mk3) for £10.36p two years ago. Remove the caliper and start checking for free movement in pads, slider pins and how hard it is to compress the piston home.
If you are doing any braking work invest in a proper caliper piston retraction toolkit. Only £18 from Amazon. Think it may be time to replace the caliper.
I have managed to sort these out before where corrosion on the outer part of the piston is jamming it. Have to make sure that the seal has not got damaged and then pump the piston out a bit. Push the gaiter forward towards the caliper exposing the part of the piston that normally sits outside the seal under the gaiter. Moisture can get trapped inside the gaiter and rust the piston plimming it up and creating a corrosion layer. You may be able to get away with clearing the rust with a stanley blade or similar and a paint brush. Once the raised corrosion is removed use red rubber grease to protect and stop the process recurring.
Brakes should work after this but if the corrosion too bad or damage to seal, there will be a leak and then plan b) = new piston and seal kit.
I successfully freed up a binding MK1 caliper, an MOT advisory (slightly binding) exactly as above post, working the piston in and out and cleaning up. It was ok then until I sold the car a year later, it’s not always going to work depending how much crud and rust has built up on them.