SOLVED IT !!!! 
After a lot of diagnostic work and testing I've finally found the fault.
The radiator fan switch is shot and the fan is not being triggered when the engine is HOT.
Before the engine is overheating (gauge showing 90c but temp is actually at 110c) the ecu is shutting down
the engine, let it cool a little and it starts again untill the same thing happens again.
Switch now hardwired (temp mod) and she runs fine, had it running for an hour yesterday and took it for a quick
blast along the road last night (only couple of miles ) but seems sweet.
Just need to get in for a MOT test now !!!
