I can't share the document, but the UK "BMW Approved Used Cars Rules & Regulations" document states:
"M Power Running in Service
... all M Power vehicles are required to have a 1,200 mile running in service...
...
Note: if a low mileage M vehicle reaches 2 years old before covering 1,200 miles, then the running in service must be carried out regardless of mileage.
To qualify to be sold through the Approved Used Car Programme an M Power car cannot have covered more than 2,000 miles before having it's running in service."