The 'extra' information in a TV signal (such as that you refer to) is usually the first thing to disappear when there's insufficient signal strength (or interference from other stations or the same, or adjacent, channels).
The current high atmospheric pressure causes problems with the reception of TV signals (including allowing foreign stations to interfere with the reception of UK ones). So your problem will probably self-clear when the pressure drops.
In the meantime, a simple signal booster is likely to fix the problem:
http://www.argos.co.uk/product/5713543
(You'd need one of these to go with it:
https://www.screwfix.com/p/fly-lead-coaxial-plug-to-plug-1m/41720 )