UK site struggling on google.co.uk

We have a .com site hosted in the UK, which is doing really well on the .com version of Google, but is absolutely nowhere on Google.co.uk.

I have done a few sites before where the opposite has sometimes happened, but that is to be expected. However, I have no idea what is happening with this one.

I have double checked to make sure that the site is physically hosted on a UK server and everything is fine. When I search for the site directly on google.co.uk it is found, so there seems to be no issue with the server location, which was my first instinct.

Having scratched my head on this one I wondered if anyone might be able to shed some light on what might be causing this peculiarity?

Thanks in advance.

Gary