hi all, further to my post about the misfire, I called BMW and they could not get me in until the 29th so I took it to a local specialist and they put the scanner on it. After about 5 minutes it came back with the faulst of a misfire on all cylinders! It drove tot he garage ok by the way!
As it had not done it since the guy reset the codes and just told me to give him a buzz if it did it again. Its been fine though since. I note the comment about the temperature and the day it went wrong was very hot - not as hot at TX thought!