Greetings,
You
might be able to do this by editing a .plist file. First download
Pref Setter, then do this:
Go to Home/Library/Safari and change the name of SearchProviders.plist.signed to SearchProviders.plist.
Open the SearchProviders.plist file with Pref Setter, click on the disclosure triangle at the top, then look for the Search String field, which is setup for Google.com. Double-click on the field at the right of that property, then substitute "google.co.uk" for the google.com portion in that field.
Save your changes and quit Pref Setter; then change the name of the file back to SearchProviders.plist.signed and restart Safari to test it. If it works, that's great. But be prepared for it not to work, since the file is supposedly signed, and Safari may just generate a new one upon restart.
If it doesn't work, you just have to wait for Inquisitor or Glims to be Snow Leopard compatible.