I think it would be a good idea to invest a few hundred pounds in legal advice.
I personally cannot see any legal recourse for discrimination by clarifying rules of a sport.
If you read the rules of golf, they by their very nature discriminate against non able bodied people. if you can't play by the rules then unfortunately you don;t play. There is nothing discriminatory about that.
The fact that the BFTA is even considering a disabled class is and honourable and positive piece of political correctness.
BFTA reps and members, might be a good idea to lobby for some concrete paid legal advice.
As for the person who is threatening legal action, if that video was used in evidence in a court case (against the BFTA) and the DSS happened to get wind of his activities...well.
Its silly for people in glass houses to throw stones.