I thought of making a puller but there's nowhere to mount one. The only other idea I had was to drive it with the handbrake on for a few miles, maybe that would generate enough heat to free it. But I've run out of time now, need to get it back on the road this weekend.
Hopefully the garage will have a bigger hammer than the one I've got.

 

Instead of a puller get a small hydraulic jack on its side between disc and suspension spring. Pack it between disc and backplate if you have too. If it still holds whack it and it may shock off.

 

Well it appears that I should have had more faith in my handbrake because without making any adjustments it passed it's MOT test yesterday!
I've now got 12 months to figure out how to remove the disc.

 

I reckon the heat and hammer method is the right one, except maybe not enough oomph.
If a part isn't worth rescuing, I've used my biggest sledgehammer to free such parts plus a blowlamp, but you'll need a big flame. Mechanics have access to oxy-acetylene with much hotter flame. Best of luck...
Leedsman.

 

Not much this side of Acet will guarentee, but MAPP and a good plumbers torch should break rust.