UPDATE: I had good news today, I went to talk to the mechanic that maintains our cars, I found out the EGR valve has been replaced but because the car is a diesel that is pre 2009 it can go through the MOT with the engine management light on. Who knew? So my plan is, put it through the MOT, hopefully pass, get the fault code read so I can sell it with a fair idea of what needs doing. Also if it passes the MOT I can run it to work and back for a couple of weeks (40 miles a day at 50-60 mph) and get everything going. Thanks for all your advice, I'll post when I'm ready to sell.