I would agree that perhaps a very small minority of British pilots would fail to obtain level 6 ICAO English, if the test is a true measure of pronunciation, structure, vocabulary, fluency, comprehension, and interaction, as defined by ICAO (for example,
http://www.caa.co.uk/docs/43/ICAO%20LPRs.pdf).
However, the DGAC English test in no way tests those measures of English competency. The DGAC English consists of a series of out-of-context ATC recordings, and if you fail to understand one or two words then you are excluded from level 6. Completely ridiculous!
Despite what others are misleadingly stating, the ICAO language requirements have nothing to do with aeronautical knowledge - their requirements are entirely a measure of linguistic competence. There is no way that a non-pilot native English speaker could ever even get close to level 6 on the DGAC test (let alone the fact that most of the test is conducted in French!!).
The DGAC has some serious thinking to do on its FCL1.028 test otherwise it is going to seriously penalise DGAC pilots on the job market.