You where one of the *lucky* seven out of what? hundreds? maybe thousands?
Britannia could have asked for anything they wanted. However, it wasn't really Britannia's choice, BAE systems have set a minima for training and requires there students to have A levels and the ability to compelte a science based degree.
Will you seriously use all you have learnt from an aeronautical engineering degree by plugging a few digits into an FMC and pressing the little "CMD A" button....oh, and a bit of flying? Most pilots come out of groundschool and ditch what they have learnt, except maybe about 5% of it. I have about 9 good GCSE's, and 3 AS Levels (not A Levels, I quit college after one year) and I am doing ATPLs and it all seems pretty straight forward, mostly GCSE stuff, trig etc. I am sure a little bit of A Level physics will crop up but I have looked at Mod 2 and still...seems pretty straight forward.
I sincerely hope that Britannia doesn't base it's selection on whether the applicant has an aeronautical engineering degree or not, but like I say, they can ask for anything, afterall, you must be academically able if you got a degree