My daughter does not think it is related to the service or oil change as on questioning she thinks it may have also happened a couple of times beforehand. I know this sounds silly but it is difficult to remember as it is only an occasional fault.
It would have been an engine oil change - but in a Mini doesn't the engine and gearbox share the same oil?
No dashboard fault lights.
Large local garage - always seemed quite reliable. We are out in the country and nearest BMW garage quite a long way away.