Simsi - 9:36 am on Oct 10, 2012 (gmt 0)
Personally yes, I would do that. I'm not sure how much clout it has but it is one more signal that the site is UK-aimed.
I've always felt it's wrong for Google to make assumptions about a site's target audience based on hosting location and dialect as one major benefit of the web is to break down International barriers. Be much better if they allowed some sort of META tag where you could specify included or excluded ISO codes but right now that's not an option so as many signals as you can throw out the better in my opinion.