maybe try a factory reset and re-tune and see if it offers you different options for areas during the first tune up...
Old Welsh Dragon has said much better than I did what I was trying to get at when asking about the region...
also maybe try swapping some leads (the fly lead and the hdmi lead and the port in the TV it goes into)
The question I would pose is
How do you know that the Youview box is tuning in to the the transmitter you think it is ?
If I put a Tunbridge Wells postcode into the ukfree.tv website it lists 3 potential transmitters Reigate, Bluebell Hill and Tunbridge Wells.
I don't know the answer only a feeling from following threads over ther past year or so that Youview doesn't always handle Transmitter selection very well
I could only work out from the areas given at the end of the tuning phase (but the names are areas not masts so it still takes some working out).
The regional channels on BBC1 (xxxxx) in the listing should give you a clue and you can also look to see if thier are any other BBC variants listed in the 900 range at the end of the epg.
Try using an in-door aerial - it's less likely to pick up the wrong transmitter and gives you a result you can compare and test against.