Anyway, I undid the lockring & took the first two rings off.
The first shock I had was that the cassette & freehub all came off the wheel in one piece.
Oooops I thought, but it turns out that the freehub was supposed to come away. But what I could not do was get the remains of the cassette of the freehub. It was firmly stuck & no matter of subtle welly would get it to budge.
I took the wheel & cassette to the shop I had bought the new one from, Merlin in Chorley.
There the mechanic, did a great trick & free of charge. Thanks Merlin. Using two chain whips one in each direction with one on the outer (smallest) gear he gave them a little jiggle and off popped the first gear.
He then repeated the process until they were all off.
Turns out the cause is having a very lightweight (for that read soft) freehub, and the cassette had eaten into the splines like a key and locked itself on.
