I've had a lot of help and advice from everyone on here and can probably be a little more specific about my problem now - symptoms as follows:
Car tries to stall when pulling away, shudders (like a bad misfire) on the move but at between 1500-2000rpm (in any gear) and blows out a lot of black smoke as you accelerate out of this rev range. After 2000rpm there is no smoke and it pulls perfectly. Fuel consumption seems reasonable at approx 44mpg average.
I did have the spanner light coming on at higher revs but a new upper inlet manifold/throttle body has eliminated this part of the fault.
Now for the interesting bit..... if I disconnect the electrical plug from the egr valve and drive the car it automatically goes into restricted power mode and so has no go above 2000ish rpm, however........with the egr disconnected I do not get the attempted stall when pulling away, nor do I get any black smoke or shudder in the 1500-2000rpm range that was previously the problem.
So, in summary:
egr connected = trying to stall, shuddering, lots of black smoke up to 2000pm but fine after
egr disconnected = runs fine up to 2000rpm (no stalling, no shudder, no smoke), but ecu puts car into restricted power so can't access the higher rev ranges
Can I assume that the egr is shagged? Or is there something else that I should be looking at?
I'm halfway to getting this car running nicely so just need to solve the last part of the puzzle!
Thanks to everyone who has helped me get this far!