When you provide us with a reading, it has to be checked by an independent data collector and compared to your historic energy consumption information to decide whether or not it looks like it falls in line with where we'd expect your meter reading to be.
If it does, they'll approve it as your official 'handover' reading, and send it to your old supplier.
If it doesn't, they'll use data from your old supplier to estimate a read they feel is more in line with your energy consumption history.