Hi zulu17
Thanks for both your messages - I will work through your suggestions & report back in due course!!
Cheers!
Have you checked to see if any birds are nesting on your aerial? 😁
When dropping the BT box out of the loop, do not take the aerial cable from the YouView box and plug it in the TV in place of the cable from box to TV (assuming you have that).
Rather, initially, just take both aerial connections from the YouView box and couple them together.
If the problem persists, only then try a cable directly from wall socket to TV. If that is OK, then you are likely looking at the slight, but not negligible, possibility of a problem with the onward cable from box to TV.
You can do this in the opposite sequence if you like, but the important thing is to test both with and without the onward cable, so you don’t erroneously diagnose a problem with the onward cable as a problem with the box.
I had this earlier in the year and a bit of AV research sent me to check the signal strength for terrestrial channels, all at 100%. Followed the suggestions that the decoders in the box can get overloaded and bought a variable attenuator (Amazon, about £6) and turned it to give me 90% signal strength and never had the problem since.