I look after the volts for our Village Hall and we just switched from EDF to npower. I was told that I'd be notified when to go read the meter for the final reading. In the event I didn't get told the switchover date in a timely way, so it turns out that between them, they've estimated what the switchover meter readings were. I only discovered this when the first bill came, today.
At the end of June to took readings but was unable to submit them until today as we had a lightning strike that took out our router, and the ISP was a bit slow in getting a new one out.
Now it turns out that the actual readings for end-June are *below* those estimated readings for end-May, when the switchover took place. I entered them anyway and it'll be interesting to see what they do with them.