You need to check that your aerial hasn't been knocked out of alignment by high winds. You also need to check, as far as is possible, that all connections from your aerial (e.g. into and out of any signal amplifier you might use, and into the back of your TV or digibox) are still firmly in place.
Then use the postcode facility here to see if there is a transmitter fault:
https://faq.external....atic/interferencePage
Also check here to see if there's any planned engineering work:
http://www.digitaluk....ial/engineering_works
If nothing there helps, it's time to upgrade your aerial. See my posts here:
http://www.theanswerb...y/Question858245.html
Chris