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Hi Jamie, I think I'm a little confused by the situation/question. If he wants users who land on the .com domain to stay on the .com domain, this is the default behaviour of a website so he could simply remove the 301 redirect. Doing this would double the maintenance and SEO work required so it's rarely a good idea unless he has a lot of resources to throw at it. Also, having 2 websites that are absolutely identical is dangerous; you won't get 'penalised' for it but the rankings would likely be pretty bad. If he were to go down the route of running 2 sites, the best way to handle this is to write content that appeals to the users in each of those locations. The most obvious difference being UK English vs US but the way content is written for each country will typically contain regional differences too.

Thank you everyone. I've followed all the good practice suggestions etc. It's still WAY back in the rankings but is making progress!