If you've the budget for it, you can buy existing UK sites with PR, make sure Google doesn't catch on that they all belong to you (hide whois, or different company/address, use different Analytics account...etc.) and link those to your existing site. Sites with decent PR often go amazingly cheap, especially if you contact someone directly rather than on a site like Flippa.
Having your own private network in this way can be one of the biggest competitive advantages you have since most people don't do this. Then potentially each site can pay its own way anyway with AdSense or however else you monetize it so over time they don't actually cost you anything.