Rodney, Actually the quote was been attributed to George Bernard Shaw, but there is no proof in his writings.
"Sometimes the inquirer asks, 'Was it Wilde or Shaw?’ The answer appears to be: both. In The Canterville Ghost (1887), Wilde wrote: ‘We have really everything in common with America nowadays except, of course, language’. However, the 1951 Treasury of Humorous Quotations (Esar & Bentley) quotes Shaw as saying: ‘England and America are two countries separated by the same language’, but without giving a source. The quote had earlier been attributed to Shaw in Reader’s Digest (November 1942).
Much the same idea occurred to Bertrand Russell (Saturday Evening Post, 3 June 1944): ‘It is a misfortune for Anglo-American friendship that the two countries are supposed to have a common language’, and in a radio talk prepared by Dylan Thomas shortly before his death (and published after it in The Listener, April 1954) - European writers and scholars in America were, he said, ‘up against the barrier of a common language’.
Inevitably this sort of dubious attribution has also been seen: ‘Winston Churchill said our two countries were divided by a common language’ (The Times, 26 January 1987; The European, 22 November 1991.) "
Like a lot of quotes, this has passed into urban legend.
Also: "What a tangled web we weave when first we practice to deceive" is often attributed to Shakespeare, but in reality was was by Sir. Walter Scott. This one is occasionally attributed to William Blake.