Well it seems it is at front, as I did a thankfully short, local journey at the weekend, and when I parked up, there was smoke pouring off my front brake pads, like a rally car. I manage to get the caliper to release by hitting it with the wheel brace, a few times, and drove home slowly, and with minimal braking.
It's off to the garage on Thursday, so I will see what they discover, hopefully it won't be too expensive.