Rated 5 out of 5 stars

If you don't want the results to be restricted strictly to UK sources (which would exclude Wikipedia, for example):

1. Edit the "google-uk.xml" file - again, WordPad is your friend;
2. Find the line near the end that starts '<os:Url type="text/html"';
3. In the quoted URL, remove '&amp;meta=cr%3DcountryUK|countryGB'

This will make the search include global results, but delivered from the google.co.uk domain, so that UK results are prioritised.

This user has a previous review of this add-on.