Originally Posted by Ralph Sir Edward
Do you mean 1922? And also such works that from 1923 to November 1956 that didn't have their US copyright renewed? (Just trying to be a purist.)
Harry's explained the 1927 date - it's to do with the change in UK copyright laws, not US one. The links I gave in my post also have very useful info.
For later (after 1927) US works, they are only out of copyright in the UK if the author died more than 70 years ago - in 1942 or earlier, as of 1st January 2013.
For pre-1923 published US works, which are all out of copyright in the US, I think they're all public domain in the UK, although one of the sites I looked at suggested that there might be some peculiarities for works from the 1920s.