Wow, Loz, how come I never noticed what kind of trouble your fishies are in?!

I am so sorry about Perry, poor thing looked really bad.

Not that it helps now anymore (well, maybe for your Gordon), but when I saw Perry's ulcers on the first page, I was thinking of PP (potassium permanganate) as a topical treatment. I have seen big fat ulcers on koi go away completely within a 10 day period when the owner put pure PP crystals or powder on their ulcers. The fish looked purple for a week around the ulcers, but they were gone after 10 days. No sign of them whatsoever.
There is no chance of you finding PP crystals or powder in the UK, is there?