Firstly, thanks for all of the helpful posts on brakes which have helped me to get this far. And for locating the service manuals at http://vsic.lotuscars.com/ which have helped no end. However I've a few questions which I'd appreciate further advice on:
So far I've got driver's side front pads out - having _really_ struggled to remove the pins with a drift (in the end I cut them with a Dremel having loosened them). The pads are OEM Ferodo DS which looks like the picture below: the outer looks OK, but the inner has ~3mm of pad left on it and is partly broken up. I'm guessing (from this and other signs, e.g. the immovable pins) that the car's been driven on winter roads a fair bit in the past and/or tracked (I bought it a year ago). In any event the discs are unevenly worn, so the job's extended to replacing those too.
Moving to the first of the rears was a similar story - though in this case I simply couldn't shift the pins at all. Ended up cutting them out with the Dremel again and now have two short stubs left in the back of the caliper. I've soaked them in WD40 and have some plans for a cunning punch adaptor to try to shift them, but if anyone has solved this problem some other way in the past I'd be grateful to hear of it. The inside of the rear disc is shown below: in this case it looks like something has seized as the surface of the disc is fairly rusty (the outside of the disc isn't) and doesn't look like it's seen a pad in a while.
Anyhow, my plan is to replace all the discs, clean everything up, make sure the calipers are moving, and reassemble. Any advice on removing those pins - and on what might have caused the condition of that rear disc - gratefully received.