Sunday when I went to leave work, car refused to start, cranked but no firing up, a few cycles of the key and she eventually went.
Oddball symptoms were temp showing full red/overheat with stone cold engine, no priming pulse from in line pump.
Having spoken to BMW they suggested a failed ECU , as did BBA and all the usual suspects, £1000 pound odd inc coding.
I think NO WAY JOSE !
So I investigate, Diagnostic showed a myriad of faults all relating to CAN bus error/DDE/DSC/ABS
Impossible I say so work through the list clearing as I go ( BMW DIS software) and think Hmmm, what do all these modules have in common ?
Out with the ETM, trace ECU(DDE) power feed, Blue relay in elec compartment in engine bay issue methinks
Remove relay and test- it clicks.... bridge power terminals on relay holder , car runs !
refit relay- non start- temp full hot and no DDE diagnostic data possible
So I removed the relay cover , inside there is the normal contactor setup and the coil trigger ( EWS 3 to low ) but lurking at the bottom hidden from view is a Zener diode, thats the culprit then !!
New relay fitted cures all £8.60 inc VAT
Moral here is , check the most basic items first
and a relay being electro-mechanical is a fairly basic thing 
just FYI in case it happens to someone else really
total cost was about an hour of my time and the new relay, I wonder if that would be true if I'd have taken it to the stealers/local indy ?
