Right, car is back with me now and the brakes are... better. Not perfect, but they're better. Apparently they're just full of air, and given that I've bled them multiple times, the local Jag specialist has bled them multiple times, and now my local Pork specialist has bled them multiple times, then that's a lot of air! Never had this issue before across multiple '2s, so it's a bit weird. PSR Automotive have done a great job in getting them better, and also giving it a go for me when they're snowed under with work on proper cars. Hopefully the brakes will get fixed for sure when the car goes to Rogue tomorrow, as they're MR2 specialists.