I am using Windows Vista and my postcode is OX5 1TF. I cannot retrieve the listings for ITV1 and ITV2, the message which appears is "No data available".

If the listings for these channels were previously available, but now they no longer appear when you download the guide data, I would suspect your epg database needs rebuilding. 

I've experienced random channels showing 'no data available' although there was data in the edit listings dialogue, a couple of times now.  The only way I found to recover was to delete the epg database in the ehome folder, and rerun TV setup including a new scan of the channels.

HTH