This has started happening recently and I've no idea why. I haven't changed anything. Some channels are always fine, and some are fine some of the time. I went through tonight and 18, 19,22, 25, 31, 35, 39, 42 and 47 are breaking up dreadfully. (I didn't go past 47 as the only other thing I look at is the news channel 231 and that's okay). Does anyone have any idea why this might be happening, please?

The first thing I always try is retuning all the channels ! I expect you've tried thay all ready?

I'd guess it's the connections somewhere on your antenna. Poor connection = poor signal strength = poor picture.
I presume your antenna hasn't moved in the wind?

Getting the same here, I assumed my aerial had moved in the bad winds a couple of weeks back.

It only really affects my non-HD BBC1 though.

Thanks for those suggestions; I retuned when it first started happening, no change. Just been down the garden to look at the aerial and there isn't any visible problem. That doesn't mean there isn't a dodgy connection, of course! If it persists I might get the Saughall Massie tv people to come and look at it. To be honest the only channels I'd miss are 25 and 47, but I'd like to get it sorted. Thanks folks.

Your TV could be latching on to the wrong transmitter, most of Greasby should using the Storeton Transmitter and is normally used with a vertically polarised aerial on Multiplexors 28, 25, 22, 23, 26, 29, 30

Some channels changed in March.

Take a look at the Digital Spy forum and the coverage checker of Digital UK. They should give you a better idea, including expected signal strengths at your location.

Your TV or set-top-box (STB) should be able to show you both the channel number (of the mux) and signal strength and digital quality of the particular program channel you are looking at. This is usually found in the set-up screen.

Quite apart from any potential antenna problems, is there any amplifier or filter in the co-ax between the two?

Finally, possibly the strangest one - Is the signal too strong?
This could overload the tuner and cause distortion of the wanted signal.

People on the 'wrong side of the hill' in Greasby sometimes latch on to the transmitter in Wales, Moel y Parc I think it's called, but I haven't had that problem fortunately. I mean, I like the Welsh language and attempted to learn it once (didn't get very far) but I have no wish to watch Pobol Y Cym - if it's still on! Will check the Digital Spy Forum and explore other options mentioned - thanks for your advice folks.