This political discussion is entirely OT here.
If the applicability of GIB is in doubt due to the clause in the Regulation it has no baring on the OPs ability to bring a claim (irrespective of the merits of it) in my view. As David-A says is an ex-EU flight on an EU carrier TO GIB. Perhaps the applicability is in doubt on flights FROM GIB but I highly doubt an airline like BA would raise a point of law on this matter in defending a claim.
To the OP, go ahead and make your claim and report back on the outcome please.