SEO example.com and example.co.uk

If do a 301 redirect then the .co.uk domain will have no SEO value for you as a 301 redirect tells the search engines that the page has moved and to use the new URL in its search results.

Basically you can't have two or more domains point to the same site in the hopes of improving your rankings. That will cause duplicate content issues which will hurt you rather then help you.

As I have posted on the identical question on Stack Overflow.

From the SitePoint FAQ on Search Engine Optimisation.

How do improve my rankings for country specific search?

To rank better in country specific search you should:

1) Use the country specific TLD

2) Host the site in that country

3) Set the geographic location for the site in Google Webmaster Tools