Recently did an ECU reset, then journeyed up to Bradford and around Mancunia- got 23.3 mpg.
For the journey home, filled the tank full again, from the warning light, reset the trip-o-meter and also added some Redex fuel cleaner.
So far, I've achieved 211 miles in just over half a tank, which is a bit of a miracle. I hope it continues like that!
Also, gonna book in with Tony B. from WIM to get a full geo done, cos the car was jumping around the place when travelling at speed on the motorway.
I'll keep ya posted, as my experiences might well serve someone else with similar problems.