I've been told from a reputable source, that is really difficult and you have to be really brilliant to be selected to take the training.
I think "brilliant" is perhaps overstating it a bit, BA aren't looking for future Nobel prize winners, they are looking for someone who is a good "fit" - round pegs for round holes, etc.... That said you need to know how to play the selection game and yes, you certainly need to have done your preparation and part of that knowing what BA are looking for.
As far as foreign nationals are concerned there are plenty of non- British EU nationals inside BA and also going through FPP. As was already pointed out you need to have the unrestricted right to live and work in the UK to apply for the FPP and it's a standard part of the BA contract. It's a right most nationals of the original EU member states possess.