The bulb holder originally had the clip holding the bulb from right to left, but the grooves snapped/wore off on the right side. The only way I could get the clip to work therefore was to switch the clip around so that it sat under the screw on the left. This was the screw I was tightening when it went pop. I might add that I didn't actually need to tighten the screw because I did the switch about three bulbs ago so I'm less than chuffed with my pointless tampering...
I've spoken to BMW who will not commit to a warranty repair until they have seen the problem themselves so I will be taking it in tomorrow.
Fego
ps - I mostly drink London Pride (or any similar ales) which costs
£2.50 a pint in the pub near my EC3 office btw...