Level 6
You make the assumption that every pilot in Europe is somehow Level 6 in English and able to dispute you a seat in a UK airliner.
That is far from true, there is a big percentage that would be unable to pass a screening/interview precissely because of the language.
Lots have level 4 or 5 ON PAPER ONLY, when it comes to the real thing probably less.
The only ones that are in big numbers able to dispute you a seat would be as some ppruner pointed out, Dutch or Scandi, which I believe learn English from a very early age, and even then, they would, in my opinion, be at disadvantage because although they have a good level of English, it is not their mother tongue, and that shows on a selection process and interview.
As for being discriminated, as somebody else pointed out, all non local lingo speakers are affected, not only you, and although not too convenient for me personally, or for you, I guess it makes sense to be able to speak it for all the reasons our colleague pointed out.
If I go to UK to work in a Uk airline I am required to speak the local lingo too, which happens to be also the aeronautical/operational language.
2006