[danielam]

I can't speak about the relative sophistication of British cryptanalysis during WWI, but Bletchley owed much of its sophistication to the Poles. The Polish Cipher Bureau was responsible for bringing mathematical and computational techniques into cryptanalysis while the French and the British were still largely employing linguistic analysis. Few realize that the Enigma was actually broken and reverse engineered by the Cipher Bureau before two new rotors were added by the Germans less than a year before the War, or that Turing's bombe was developed from Rejewski's bomba.

[richieb]

The Poles certainly got the ball rolling (see http://www.codesandciphers.org.uk/virtualbp/poles/poles.htm), but the organization at Bletchley Park took decryption and analysis of Enigma traffic to an industrial scale. By the end of war Bletchley employed around 10,000 people. See Alan Turing's and Gordon Welchman's biographies for more details.