UPDATE: I tried removing the old axle and bearings last night. One end of the axle had gone a bit out-of-shape at the point where the axle spacers and bearing cartridge had to pass over the get them off. I had to use a bit of brute force with a hammer and some mole grips, which it turns out was a really bad idea. Got them off after about 3 hours but mashed up the bearing cartridge in the process. You live and learn.
Still, it gives me an excuse to upgrade to ceramic bearings. I've found some on chainreaction for £28. These are the right size right? They're 6001LLB, (12 x 28 x 8mm)