Cleaned and tested fuel pump, engine management and ignition relays.
Roadtested this morning, fine for about a mile, then messed about for about a mile and a half and after that behaved perfectly for about 5 miles back to the workshop.
The problem seems evident only whilst warming up.
It always cuts cleanly for about 2 seconds and then picks up cleanly afterwards, it is only the time betweens drop outs that is random.
It feels like the PCM is crashing and doing a reboot/restart.
There appears to be no relationship between how hard it is working and the cutting out, which to me makes it seem like it is not fuel supply related.
Shaun