Half drained the CH, cut the leaking pipe below the damage, and removed the old radiator.
Then spent an hour and a half prising tiles off the walls. They are going to need skimming before re-tiling as some plaster has come off. Bah. That puts the project back until I find a plasterer, although I will leave the old bath in until it's done, so I am still functional (just no showers, and only the downstairs bog and basin).