Chris

How long have you lived there? It probably is in the loft, but if you've never seen it and didn't take any action to change it for digital switchover, then the solution to your problem is probably as described earlier in the thread by nodrogd. i.e. You don't have the right aerial to receive all the channels being broadcast from your transmitter.

Check in the loft. When you find the aerial, look at the front end of it. There will be a coloured plastic bung in the end. Post back and tell us what colour the bung is.

While you're at it, also tell us which direction it is pointing.