A brief update on the cam sensor returning an "invalid" reading and ridiculous cam angle number through Pscan on my rover mini.
Turns out the flywheel had moved 140 deg out (and I suspect had been fitted by last numpty at 180deg out) with broken key washer and loose bolt with very messy boss taper. Amazingly the thing was still struggling, running and idling until it got so far out it was trying to fire about 150 deg BTDC then gave up.
Sorted new boss, flywheel mounted correctly and it all works sweetly with everything reading OK.
Lesson learnt - if cam sensor doesn't read but cam and crank sensor and wiring (and everything else!) are all OK, suspect flywheel is 180deg out or at least significantly out so MEMS thinks the cam reading is invalid. Actually the cam reading can be right (as in my case) and the crank reading wrong but it automatically ignores the cam sensor in favour of crank priority.
Loose flywheels are much more common on minis than I thought...
Total success for Pscan so far - now to program a new to me spare key fob