My neighbour (also bikers) stopped for someone between Westbury and Warminster who ran out of fuel, they were most embarrassed and were given a lift to the nearest fuel station - only another mile!
I saw someone the other day stopped but they seemed okay and I had to be somewhere, normally I would stop, especially if they looked in distress (pi$$ed off) or had the bike in bits.

I would be happy to add my number to a list of contacts who would happily rescue a fellow biker - take them tools, fuel or even rescue the bike if my neighbours van was available. Did this with a 4x4 group in the past in case anyone got stuck in the mud.