Today I received a new clutch cable from http://www.nsamotorcycles.co.uk/ and fitted it to the engine before dropping the latter back into the frame. I've always found fitting a clutch cable quite fiddly - with my head upside down - so with it out of the frame it was much easier.
I'd also bought some rubber cable ties from Nick - at NSA based just outside Beccles, Suffolk - and can recommend him for the quality of his spares and fast service. Thank you, Nick!
Unfortunately, both of these were very rusty and pitted, and ought to be replaced, but to keep costs down - for the time being - I've sprayed the silencer and pipe with silver heat-proof paint.
My apology to those purists amongst you, but I'll repl;ace the parts when I can afford £150 or whatever they cost these days. Not cheap, I know.