Little question about domains

I've got a site based on the dentist method posted a while ago but it targets the restaurant niche instead.

Now my site doesn't exactly have a lot of information; it's got a slider that says"Best Restaurants in Town, Quality food rah rah rah" and a few pages going over what italian food is , turkish food is etc but nothing about those in the area.

Now i only have the .com domain however the .co.uk is available (I'm targeting the UK).

The .com is currently rank #8 in google.com but #31 in google.co.uk.

I'm guessing instead of backlinking UK sites like mad it would be easier to invest $4.99 in the .co.uk domain.

My question is how do i go about doing it?

Do i simply redirect the .co.uk to the .com as this is already established? Or do i changed the site to have the .co.uk as the primary domain and what effects will this have on my rank already?

Hope someone can give me some advice!

While it's good to have the .co.uk to simply let your audience know that your site is uk based you don't need it to improve rankings on google uk.

I would make sure that you have uk set in webmaster tools under geo location. I would also look into earning more links from uk sites.