To view other ITV regions on Sky Digital, you have to add them to your 'other channels' list. Try
www.wildsat.com/astra.htm and follow the 'manual tuning' instructions for adding channels as indicated at the bottom of the page.
Basically you enter the transponder frequency and polarity, and the appropriate FEC and symbol rate (all are stated on the link). Then 'search for channels' and tag the ones you want - they will then be added to your 'other channels' option.