It really doesn't matter where your host is based. I used HostExcellence and I live in the UK and I have had no problems whatsoever. I just e-mail them if I do and they respond within in hour. I have also used GoDaddy in the past with no problems.
Just because you are based in the UK, you DON'T need a UK host.
24/7 tech support is a lot more important than location. I've been using Host Excellence for 7 years now and haven't found any reason to change.
Their associated service - IXWebhosting - offers really good value for those who only have one site but need the option fo another dedicated IP address. Their tech support has been really helpful to those to whom I have recommended this service as you will see here...
Most tech support people don't seem to understand how iWeb creates sites and can be rather unhelpful.
One of the main advantages of the above mentioned services is the fact that they allow you to create a root folder with the same name as your site in iWeb. This goes a long way to helping you understand the concept of the root folder and the file/folder structure on the server.
IXWebhosting also has a tutorial on how to migrate from MobileMe to their hosting service that a have posted on my blog.