hi I hold a passport from a a recently joined EU country and I was successful at the assessment with BA for Longhaul. I think they doublechecked when I was at the interview so I assume If I got it the passport is ok.
I already had my National Insurence Number with me. In order to apply for N.I. I think U have to be in UK already as U have to provide some proof of address and other documents in order to get it.
hope this helps !
and good luck!