Thanks Monte for the suggestion - I may just take it up - I think it will be cheaper in the long run.
I think it is more than just the relay - I didn't see any of the appropriate wiring or connections at all. As I said ages ago, when I first got the bike, I thought it had a bit of hard life - though I didn't mention that the wiring was shot. I'm not sure what the previous owner had done, but he had made it into a bit of cafe racer and ultimately it required a lot of new wiring.
Next weekend, apart from taking the bike out for a lengthy test ride (its a hard job, but someone has to do it), I want to take the fairing off and have a really good look at the hazard system and see if the wiring has just been taped up somewhere that I didn't see at a cursory glance.