Jonathan,
I'm having similar problems with my 3.5 EFi Disco. I am also in the Durham area (Consett to be precise) so was just wondering if as a fair amount of time has passed if you managed to get rid of your gremlins.
My problems are it will drive ok, but under powered for a V8, but at idle runs rough, and just had the awful event of it not starting for 5 minutes then coughing and spluttering unless the pedal was off idle.
I love my Disco but wish i'd stuck with diesels - swaps anyone?