OK, back from the BMW dealer's part desk. One of the dealer mechanics took a look, then went and found the printed diagrams for the car to work out which was which.
According to them, the two relays towards the centre line, under the smaller cover, are Fuel Pump (centre slot) and DME (engine mangement, right slot). They are identical relays (and I think pretty common over the BMW range from comments of parts desk man).
The space to the left would house a relay for the O2 sensors if needed by the car (not sure which markets that would be, possibly California??. My car would need such sensors for the catalyst and EU emission regulations, but I guess a different system).
They are only 5 pounds each (=~US$10) and held in stock by the local dealer's parts desk, so to save further hassle, I plan to swap both.
As my problem is intermittant, I can't be certain the swap fixes the problem. All I can do is wait to see if it recurs.
Reminder - my car is a 1998 UK/EU, M44 engine, manual.
- Nige |