It is the clubs responsibility to check that all racers are BRCA members
whenever they race at their clubs if they themselves are BRCA affiliated. That goes for club rounds or bigger/regional events.
Truth is, for good or bad, clubs get used to seeing people around, and once the licence renewals period is done, and checks are made around that time, they might rightly or wrongly assume that racers have their licence sorted. Correct me if I'm wrong, but you've raced at WORM, Yatton, Tiverton and Caldicot possibly this year...so that's 4 different clubs that have failed to check you in it!
Letter of the law (as far as I can understand):
You don't have any legitimate entry's/results so far this year, so entering on Sunday will mean you only have 1 result to use for a grading.
Entering on Sunday is reliant on the club being satisfied that your now a member, and that would mean them either seeing your card, them being satisfied that you've presented something legitimate confirming your membership is being processed, or them having contacted the BRCA themselves to ensure it's being processed.
As for my personal thoughts...if you drop out that's points for me!!!
But it's toy cars...and only a hobby...is it really a problem???
As an aside to that...do you/did you intend to use your F grading for nationals/end of season entry next year? If you didn't then it's not really an issue anyway.