My thompson digital recorder stopped receiving channels effectively?

I've been living in a flat in Manchester, UK for 6 months with perfectly fine reception for my digital recorder and additional top up tv channels. However for the last month my box has failed to maintain a good signal for itv, channel four, five and associated freeview channels and topup channels. It's driving me crazy and I switched to an old normal freeview box - but found the same problem - particularly between the hours of 5pm and 10pm.
As far as I know nothing has happened to my outside aerial, but even the analogue channels are behaving oddly with interference lines running up and down the screen at regular intervals.

Anybody got any ideas what is causing this?