Doh!
After suffering for a few days trying to find a solution to my problem (boiler cuts flames after approx 3 seconds then goes through complete sequence again, lighting flames, cutting flames, etc) I finally came to the conclusion that it must be the HT lead. I had a look and measured the resistance: 4.6K instead of the 10K quoted previously in this newsgroup. Had a gentle wiggle about with it, but it turned out a fatal mistake, it was very brittle at one of the ends and now the boiler won't light at all! :/
So the question is, where can I obtain a new HT lead? I live in Bucks and work in London, so any shops I can walk into tomorrow is a big plus, otherwise it will have to be online.
Yours freezing (and smelly in a few days)
Q.