Mostly it's the same, but if you are targeting google.co.uk you will need to pay attention to the small details.
1. Language - the language is the same, don't worry about having to sound like someone from Mary Poppins, there is really little difference and colloquialisms really have no place in writing for a broad audience.
2. Spelling - watch your spelling, we do things a little different over here. Watch, your z's and s's and maybe get it read by a UK copywriter. This is important, if you have US spellings, you are telling google it's for a US audience!
3. GEO Stuff - You can specify the location you are targeting in webmaster tools, obviously, but you can also do more. Make sure the UK address is on the site, make sure you use the correct monetary units and any other localisation that is important to the business.
4. Link Building - You will want to find some UK link sources, ideally topically relevant ones as well. That's not to say you can't get links from the US, it's no biggy but you want to make sure you have some quality UK ones.
Really, it's not much different, just the smaller details so don't sweat it to much.
Matt Cutts made this video about releasing the same content over multiple top level domains (TLDs) yesterday I think and whilst it is a different subject there are some good indicators of what they are looking for
http://www.youtube.com/watch?v=Ets7nHOV1Yo
Cheers!
Marcus

