Drove up to the Lake District Sunday/Monday and the Plus 8 didn't miss a beat, went to use the car on Wednesday and it wouldn't run, plentyl of fuel pressure and spark but it cut out straight away. To cut a long story short two days of torrential rain had flooded the ECU. I disconnected the ECU and water literally poured out. I took the ECU case apart, dried it and left it in the sun for a couple of hours before reassembling and refitting, sadly it was still the same. Took it apart again and dried it with a hair drier. Reassembled and it worked beautifully.
Next job when I get home from Harrogate is to try and find out where the water is getting in and stop it, think I'll also drill a couple of drain holes in the bottom of the ECU case and spray the circuit board with ACF-50. Any other suggestions?
With thanks to Brett at BHM for help over the phone and Keith from BHM for offering to bring an ECU up to Harrogate.