OK - found a dealer with DRBIII and the diagnosis was the DRIVE MOTOR (05161797AA).
Sadly they wanted nearly £600 to get the part and replace it so I went to a local breakers yard an got one there.

I've fitted the motor but still no joy - now before I go back to the breakers yard (I realise the motor could be dodgy), I wanted to check something. The DRBIII reports Diagnostic Trouble Codes (DTCs), will I need the dealer to clear these codes - even if I bought a brand new motor do the DTC codes need to be cleared and the "system" reset?

Cheers