So, today I drained the oil and sieved it which didn’t show anything and the tiny bits at the bottom of the drain pan seemed to be road muck fallen from outside of bottom of engine - they mostly squished away to nothing when rubbed between fingers and what was left didn’t look shiny or stick to a magnet.
It was quite an effort to get the clutch cover off, after removing all the fasteners it still took 2 hours of careful prising, head scratching and a whisky to get it off.
I got the clutch plates out and the problem is the clutch lifter bearing as I’d guessed. 1mm of sideways play, rolls as thought filled with grit, and you can seen in the close-up photo below after cleaning it there’s lots of tiny metal fragments washed off. (Bearings and cage look intact, so no big chunks missing.)
Clutch plates are still within wear limits, probably a bit more than 50% worn, (I did wonder being as I’ve done near;y 46k miles) but I’ll replace them whist I’m at it, and the springs, and the o-rings for the shafts that go into/through the casing.
Now the difficult bit starts… removing the old gasket, but that’s for another day. Got beer and curry to consume tonight 