One reason why the election campaign has begun with no agreement on TV debates is the division over which parties should be included. The broadcasters failed to invite the Greens despite the party recently outpolling the Lib Dems and finishing ahead of them in the European elections. In the hope of splitting the left, the Tories have supported the Greens' inclusion, but Labour has refused to do so. A source recently told the Independent: "We are not going to tell the broadcasters who they should invite. We want these debates to happen and so we don’t want to complicate it. It’s not about self-interest."

But in an interview with me in this week's NS, Sadiq Khan, the shadow justice secretary, supports the inclusion of the Greens alongside Ukip in any debates. The Tooting MP, who heads a Labour electoral unit devoted to combating Natalie Bennett's party, told me:

I think they should happen and I think they [the Greens and Ukip] should be included. I’m relishing them, I think it’s an opportunity for the country to see Ed Miliband, to hear and see his passion, to hear and see the vision he has for the country and to hear and see that he thinks the best of the British public. I’m not sure why Cameron is so scared, I don’t understand why his advisers are bottling it. What the British public deserve to see is all the leaders, and that includes Natalie Bennett, by the way, having a debate about their vision for the country, their analysis of the last five years, an explanation from Cameron and Clegg how the deficit is still £200bn more than they predicted. Cameron’s scared to have a press conference, so you can understand why he’s scared to have a debate with Ed Miliband.

Supports proportional representation

Elsewhere in the interview, Khan, who is responsible for constitutional matters as shadow justice secretary, supports the introduction of proportional representation for general elections - a stance not shared with Labour. He said:

I’ve always been a PR supporter ... It means everyone has a stake in the outcome of the result. Rather than people having to vote tactically, they are voting knowing that they will have an effect on who wins the election. I meet too many people who vote for negative reasons, rather than for positive reasons. If we have a PR system it could, for example, lead to higher turnout. I believe in us being citizens, rather than consumers, and one of the ways that people will turn from being consumers into citizens is thinking that their vote counts and that will lead to that active citizenship, rather than this passive consumerism that there is now.

Backs BAME candidate shortlists

Khan, one of Labour's few senior ethnic minority politicians, also backed the introduction of partial shortlists for black, Asian and minority ethnic candidates (BAME) after statistics showed just one non-white candidate had been selected to replace the 34 Labour MPs standing down.

My personal opinion and the formulation that I have, and it’s not Labour Party policy, is a hybrid system, so you have some seats in which either half the candidates can be women and/or ethnic minority men or women. But obviously we’re now into the long campaign, time doesn’t allow for an eight-week selection process. I think the NEC needs to think about the fact that as a party we’re at our best when we look like the communities that we seek to represent.

As shadow London minister, Khan slowed down the selection process in order to ensure that eight of Labour's 12 target seat candidates in the capital were women and four were BAME.

On standing to be Mayor of London: "It's a job I'd love to do one day"

Khan, who is regarded by Labour MPs as almost certain to stand to be the party's London mayoral candidate this summer, told me that it was a job he would "love to do one day". But he warned those who have already declared their candidacies that the party would "not forgive" them if they were "distracted" from the general election.