It seems the headlight failure last night wasn't quite as simple as first thought. Having lost both dipped beam headlights last night, I found both bulbs were blown (both were working when I set off). I now have:
- new bulbs in both dipped beam lights
- headlights pop up when headlights switched on
- no dipped beam when switched on
- tail lights working normally
- when full beam is turned on, all four headlights illuminate (ie including dipped beam bulbs)
- main beam won't stay on, it will only flash as long as the column stalk is pulled (regardless of whether column stalk is pulled one step or both)
- 2*20A fuses on the lighting circuit are fine

I took it to the local (to work) Honda dealer in Milton Keynes to see if they could do anything with the relay (originally diagnosed as the problem) - they took it out of the circuit and shorted the terminals - no better. Given they had to ask where the fuse box was they clearly weren't specialists, but I'm reasonably confident the relay's OK.

Over to you guys - anyone got any ideas of what might be up? I'm baffled.

Cheers,
Rich