Thank you for all your comments!
I purchased the monster from Berry Brook in Exminster, and I'm based in Chelmsford, Essex - and there's quite a drive between the two! Melvyn Rutter is just down the road, so I might pop by there later today to ask his opinion as the car's likely to be serviced there anyway.
To clarify (more meat on the bone etc), the noise occurs when engaging first, either up or down the box (usually down), when I bring up the clutch pedal (however I do it). The clutch is significantly heavier than I've experienced in other cars (including cars with racing clutches) and very much on/off.
