Measure the mounting holes on both, but I'd be surprised if they're the same. The 1200 uses big calipers and they won't even fit on the B6. A GS500 caliper or a B6 caliper may work, and I'm pretty sure the 250 uses the same caliper as the single disc B4. Not sure how common a single disc B4 is in the UK, but that's all we got here in the USA, so if you can find one from a Yank parting out a B4, that should do... but double check the mounting hole distances on those too, just to be sure.