Well, it seems to have worked out okay - the full service was £114, including 8 platinum plugs, from the Alfa Dealer they assured me (they said they were the only source for the correct plugs, sound believable...maybe I should have a look). Does anyone know what they should be marked with?
They didn't try and sell me any other work, though they pointed out a rocker cover gasket leak, and (correctly) recommended a cambelt renewal (Iíll get that done next pay day at an Alfa specialist).
I asked them for the old plugs, they looked okay, just the gaps were very wide, looks like nearly 2mm.
Anyway - it looks like a very cheap way to get the plugs! I'm satisfied.