activeco - 9:32 pm on Jan 26, 2007 (gmt 0)
In some cases there are canonical issues involved.
If you have .com/.net/.org, etc AND co.uk., especially with (near) duplicate content, the co.uk (or even other tld) could be picked as the canonical one and the other excluded from the UK index. That's why you can't see it with site:domain.com query.
Check the unique phrases from your root page and see which domain returns it (in the UK search).