Aha - Plusgas, I hadn't thought of that, thanks for the tip. However, a chum who used to be an engineer in a huge factory with massive paper-making machinery told me yesterday that if they had metal that would not budge they gave it some heat, so everything expanded and that seemed to work. So after a night of soaking in GT85 and another unsuccessful trip to LBS, I brought it home and gave it full welly with a camping gas stove, to the point that the oil and grease particles in the cassette were in flames and I had to blow them out. Gave it five minutes. Bunged it in the vice to hold the removal tool, wrapped the chain whip round and gave a light tug. Came off a treat. Couldn't believe it. Am now waiting for it all to cool down, and the feeling of euphoria to pass. But Plusgas goes on the shopping list.