I've just gotten around to solving this little niggle; having google search google.com by default instead of google.co.uk was one of those little annoyances that I was just living with.

Today I found a solution on Chrome Bug 1521 on Comment 39

• Quit Chrome
• Open \~/Library/Application Support/Google/Chrome/Local State in your favorite text editor.
• Search for the strings 'last_known_google_url' and 'last_prompted_google_url' adn replace their values to your preferred Google base URL (e.g. www.google.com)
• Save and start chrome back up.

Yep, that works!