Connections across the water are excellent these days, so for the majority of websites you won't notice any difference hosting in the US rather than the UK. You might be talking about a 1-3 second difference (if even) in loading times.
It may be worth checking with the hosting provider to see if their data centre has good connections with either Europe or the UK.
Some people believe that the location of an IP address, be it UK or otherwise, affects how Google lists your website, i.e. if your website is hosted in the UK you will be listed in Google UK etc. As far as I know, Google doesn't release much information on how they work, so this could be speculation but something worth considering.
Another thing to consider are any Data Protection Act implications, if it affects you.
Again, most of this is probably overkill for you but it's worth knowing.