It sounds like the Google algorithm isn't recognising your UK targeted content, although you should still appear unless someone selects "Pages From The UK". The default search option does give extra weight to local sites, although does not exclude non-UK sites.
You may want to consider setting up a .co.uk microsite with unique UK specific content, hosted in Britain. Alternatively you could have a subdomain of uk.domain.com or subfolder of domain.com/uk/ and build links into the site from UK related websites.
If you're seriously interested in attracting UK/European consumers, SES London 2007
would be invaluable to you.