Also, depending where you are in the country, it's possible that high atmospheric pressure is the issue.
I am getting the same issue. Perfect picture on TV but only 48% signal strength on BT TV. Odd as the TV is connected through the BT TV box. Will try an attenuator.
An attenuator would not help in your case, its only any help if the signal level is showing 95% or above, and usually 100% (it cannot display an overload status).
TVs are designed to work over a very large signal range, and they can also tolerate higher error rates as most do not have to record the data stream.
What level of strength & quality does your TV show?
It may seem odd but if your signal strength is very high it can actually overload the tuners and they then show a low strength figure. This isn't too likely in your case but getting the TV's figures could clear this up.
I found the way to check signal strength, 63ish /100 ish (Ch 12 not 114) but alas, having already re-tuned and lost signals, can only get low quality, (not HD) so I'm rather hoping that the "high pressure" goes away and when I next re-tune they (HD channels) come back!! I guess something may have happened to my account and my HD being turned off?? So I may check on that (only just thought that MAY be a reason...)
I took up (HD) with BT:: What's the deal with having to pay "extra" for HD reception? When were NON HD TV's last made, quite some time back, I'm assuming.
I still never get a CHAT button on my BT homepage??
Sky and Virgin charge extra for HD but this shouldn't affect terrestrial channels on BT as they're broadcast via Freeview.