Can you tell us the figures for signal strength & signal quality for both BBc & ITV and is it the HD or SD channels?
bbc signal strength & quality both around 95
itv both around 40
Well that'll certainly explain the ITV issue.
I'm surprised you don't get the occassional breakup on BBC with a quality of less than 100.
When you do a retune do you get the option of different regions to tune to?
Is this a new problem or have you only just got YouView?
What about your TV, that'll probably have some signal strength & quality figures somewhere in the setup? That would be useful too.