OK at last I have the engine starting reliably from cold. This was with the help of Marine Engine Services/Primrose Engineering (Richard, Sue and Hayden. In short my governor rail was sticking in the 'fuel off' position. I came to the belief that it was something to do with one of the high pressure fuel pumps but it turned out to be the nylon/plastic "751-10288 GOVERNOR SLEEVE" that was doing the jamming (only when cold).