Thanks dudes. I finally decided to fill in both and let them pick the bones out of it! I've enclosed a photocopy of their letter telling me to claim IB and an explanation of why I completed both.
Personally, I don't like being referred to as a 'dude' which is normally taken to be dude (as in "dandy") noun : a man who is much concerned with his dress and appearance .
I am neither male, nor I am I overly concerned with my dress and appearance.
Others may be happy being referred to as 'dudes', but I am not.