Aaaah, I know that letter, got it this week too. My situation though is different, I already have a job garantuee with another airline in another country (something to do with a blue swan). And it was nice if I would be hired. It just wasn't ment to be.
But I just like to say the following. As you already noticed, you are not the only-one that has been rejected. But then again, BA isn't the only airline. It is just how eager you are to become a pilot. If it is the one and only thing you'd like to do, go try somewhere else. I don't know how the opportunities are in England, so I can't really judge that. But I'm for sure you have to follow your dreams. I did too, and I have an CPL/IR with ME now, and it is the best thing that could have happened to me.
Hope that you make the right decission, and that it may be your own decission. Nobody can do that for you..
Best of luck an regards
JBravo