Now this is assuming I've read my Haynes Manual correctly

It appears I can remove the caliper and position out of the way of the disc by removing the two 17mm bolts behind the disc instead of taking the caliper apart.

Despite trying some WD40 24 hours earlier on the bolt, the bottom one just won't budge.

Is this a common problem and is there any easy solution? I'm trying to avoid having to take this into a garage to get access on a ramp

You need to get more leverage onto your socket wrench. A stolen bit of scaffold pole works wonders. Try and stand on it.

Try tightening a little then loosening again, with WD40/Copperslip covering it.

Try also hitting the wrench with a hammer - the shock might break the grip of the rust.

One thing to avoid is taking edges off the bolt - so make sure the socket is fully on the bolt head before hitting.

You could also try applying some heat, but that requires some skill.

Make sure you apply copper grease to all bolts before reassembly.

never really had a problem.usually undo fairly easily TBH.
levrage and wd40 is best.i have a breaker bar for just such a situation.everbody should have one.
about 10-12 from halfords IIRC

Cheers for the ideas, I'll give it another crack tomorrow.