Are you talking about digital terrestial broadcasts (i.e. Freeview).
If so (and I get signals from Winter Hill) there have been periods recently when the ITV channels' MUX has been relaying lower than average signal strength.
As a result you could receive audio but no picture; however, in recent weeks, the signals have improved somewhat and the pictures can be viewed, albeit with the occasional freeze for a short time.
The problem has also been noted in other areas of the country.