Keep .co.uk, but allow personalisation
I think you should keep .co.uk, but there are an increasing number of stories covering an expanding field of interests. There are also a number of people that complain that story X or story Y has no place in elReg.
Maybe the solution is to allow visitors to set preferences about which stories are included. US specific stories, UK specific stories, non-IT politics, funnies, etc.
When a user with no cookie arrives, maybe a default set of stories could be presented depending on their geo IP, with a clear option to change the selection.
Whatever the solution chosen... keep up the good work!