But what is the point in inviting him to a debate when he won't contribute anything, by his own personal policy of not commenting on policy? What is he meant to be quizzed on, how can he reasonably challenge the other two leaders when putting forward no solutions of his own?
I agree that if UKIP have sufficient support AND are willing to debate policy then there is perhaps merit in inviting him. At present there is none. Imagine you were interviewing four prospective managers for your football club, and one of them said that he had no intention of revealing what kind of football he'd play, or what kind of vision he'd have, or what his transfer policy would be. However he would be prepared to carp at the other three when they were asked those very questions. Would you give him the time of day?
Because he is the leader of a major political party in this country. Let him prove himself I say.