"What are you afraid of, boys?"

That's the question my colleagues in the Green Party south of the border are asking Mr Cameron, Mr Miliband, Mr Clegg and Mr Farage, the four middle aged men in suits you can expect to see on your screens in the main election debates this spring.

The poster campaign which asks this question doesn't need to show those four faces, but instead shows Caroline Lucas, the first Green MP, and the leader of the Green Party of England and Wales Natalie Bennett.

The implied contrast speaks for itself, and even as another middle aged man in a suit I can recognise that when I see it.

But of course it's not just gender balance that would benefit from bringing a Green voice into those televised debates.

It would give voters a fair reflection of a wider range of arguments about the political choices the country faces.

All four of the parties the broadcasters already have on the list are signed up to one version of austerity or another - effectively committed to keep punishing the most vulnerable people in our society for the failures of banking and big business.

None of them intends to introduce meaningful taxes on unearned wealth, to close the gap between the richest and the rest.

Just the Greens.

None of them intends to create a welfare system worthy of the name, in which everyone's dignity matters.

Just the Greens.

None of them intends to cut energy bills by finally getting serious investment into reducing energy waste.

Just the Greens.

None of them intends to bring public services like the railways back into public ownership.

Just the Greens.

And these are popular policies - when people are asked to say how they would vote on policies only, like at the voteforpolicies.org.uk website, it's the Green agenda which ends up on top.

Only the ridiculously unfair Westminster voting system, and the massive donations bigger parties get from big business and wealthy individuals, skew the system in their favour.

No wonder they have no plans to close the wealth gap.

But whatever you think of that case, there's a basic democratic argument at stake too.

Either the debates are about who'll be the next Prime Minister, in which case only two men will have a sterile debate about the cigarette paper's worth of a difference between them, or they are about all the ideas on offer and all the parties which might have influence in the next Parliament.

If that's the case, there is no excuse for including the LibDems and UKIP, but keeping the Greens out.

Indeed the recent and ongoing surge in Green membership has seen the combined membership of the Greens in England, Wales and Scotland outstrip both those parties.

With tens of thousands of new members, and our opinion polling also on the rise, it's time that the broadcasters did the right thing by their viewers, and pulled out a chair for the Greens at the leader debates this year.