[urq] Weird clutch

[spot.ontheroad]

A long time ago I had an issue with a crap clutch (LuK) which I sorted by swapping for a Sachs. Problem solved.
I now have another weird problem with the clutch.
Sometimes when maybe sitting in traffic if my foot lingers on the clutch pedal for any length of time the clutch will suddenly engage and the car will try to surge forwards. The only thing to do when this happens is wrench it out of gear or if there is enough space to the car in front, lift off theclucth and imediately press again.
The car has has a new master cylinder, new slave cylinder, new pipe connecting the two. It has been bled and bled again. No air appears to be in the fluid.
I have checked to see if the over-centre spring mechanism is doing anything odd but is does not seem to be.
Any ideas? All suggestions gratefully received.

Cheers

Keith

'87 WR (RHD UK spec)