Redirect to a uk domain

My website is Lincoln.ie and this company is currently in the process of setting up an office in the UK. I'm looking for a developer to basically ensure a copy of the site (Irish one) appears on the UK domain additionally.

When a user logs on to the UK site Id like them to think they are still on a UK site (ie it doesn't redirect to the Lincoln.ie site)

I hope this makes sense! It's essentially a quick fix before we set up a UK website.