so you've had no high winds, strong rain, or anything else which might affect your aerial, the trees, or the transmitter aerial then ?
Do you know which transmitter or relay your signals come from ? The Digital UK website has some technical pages (you enter your postcode and house number, and then 'tick' the box indicating you are in the aerial installation business, and it gives more info, dates, and some notes on what changes are made).
Here in 'Granadaland' (I'm in N Wales, but depending on where you live, signals come from HTV [ITV Wales], Central [Birmingham] or Granada [Manchester], so aerials point in all sorts of directions) the switchover took place in 2009, but there is still some work to do in September 2011 for Granada, and to 2013 for both the other regions.
Many of the 'follow up' jobs after digital switchover were to alter transmitter coverage patterns (to cut down on interference) and some were to turn off channels (the top channels like 67, 66 and maybe a few close by will be sold off in the next few years for mobile phone networks).
Once all the regions have switched it will be possible to pump up the transmitter power again.
When there were both analogue and digital signals, from Winter Hill, the analogue channels mostly used 500 KW output power while the digital signals were mostly 50 KW, and one was 12.5 KW. Now that the analogue transmissions are off, they have increased the power to 100 KW except for one, COM6 (I assume it is 'commercial mux 6' because they renamed them from A B C D and 1 2 to give 3 for commercial channels [4,5,6] and 3 for public sector broadcasting [1, 2, 3]). Would you believe it but COM6 is still 12.5 KW and carries Film4
(also carries Yesterday, 4Music, Viva, ITV4. Russia Today, Al Jazeera, and a number of adult junk channels, plus some radio stations like The Hits, Kerrang, Smash Hits!, Kiss, heat,
Magic and Smooth Radio.
No proof that Film 4 is on a lower power transmission in your area, of course, but it might be the case.