There is an air of absurdity to the Ofcom ruling that the Green Party are not a major political party but UKIP are.
Everyone seems to bring their own highly biased view of what should entitle a party leader to take part in a televised debate. Usually it is the qualification that ensures their own favoured party has a place and cuts off another party.
To my mind, the key determinant should be the number of candidates a party is standing. There was (and perhaps still is) a understanding that any party standing 50 candidates at a General Election is entitled to a party Political Broadcast.
The same principle should apply to the Leaders Debates. Not to do so gives a catch 22 situation where a party, particularly a smaller party is not given the opportunity to increase its support and then the failure to increase support is in turn is used as the justification for not giving it the Party the opportunity to increase support.