As a result of the line closure to rectify the OHLE issues, the last EMT service into Norwich tonight (public timetabled to arrive 23.18) seems to have been started from Sheffield.
Over the last few weeks there have been rather a lot of services towards Norwich terminated short at Ely to maintain timetable on the return journey, not just for the incidents described by 'dk1'.
The services are generally 2 x 2 cars north west of Nottingham, almost invariably 2 car Nottingham - Norwich so I guess that the extra unit at Nottingham can be used to create flexibility (crew availability permitting).
I guess that some of the times this happens there will only be a single 2 car unit for the service north-west of Nottingham?