I haven't had a chance to have a look yet but reading through things there is 2 switches on the clutch. The first is for (push the clutch in to start). I found out about this one when trying to start my engine for the first time.
The second switch is the clutch switch, which I believe from reading and looking on my wiring diagram go's to the cruse control (push clutch in turns off) if I'm right.
So my symptoms are when I put it into gear the revs go up. Reading about this it is not picking up on the Switch so the ESU is compensating for it thinking it is going to stall I think.
I did also read something about it over fuelling when they don't work.
I will try to bypass it to start with to see iv the revs change then if they don't I will have to try and squeeze down into the foot well and try and fit this switch.
https://www.flickr.com/photos/124541083@N02/
https://haynes.co.uk/forums/showthread.php?t=13262