There is a pretty good install guide at
http://knoppmythwiki.homelinux.org/index.php?page=UKMythConfig
I had to do a few things slightly different in it, but it was spot on for getting the channels setup.
I'm located in Belfast, so my settings would be differnt from yours, but the jist is you go to select the alternative UK Radiotimes grabber, hit finish on that screen then hit Alt+Tab to get to the console, the console should read somethinng along the lines of
Enter channel name or . to end.
You Enter BBC1, then it will ask you to enter your region (BBC NI, BBC scotland, etc etc).
Then you enter the rest of your channels. If your not sure of the names you can just go to the radio times website, login, and check was it gives ya. I had a problem with ITV, as it is UTV over here, but listed as Ulster.
The rest of the steps are in that guide anyways, good luck, and if u run into problems, send me a message.
--
Dave