Mr Miliband raised the issue of open primaries in a brief passage in his recent article for the New Statesman magazine (the one that prompted stories saying he was attacking his brother, Ed). I asked him to elaborate when he met regional journalists to discuss the commission on youth unemployment he had been chairing (I've also written about youth unemployment by the way - see this week's Post).

Mr Miliband said: "I think for the Labour Party locally, a candidate who is selected having engaged with tens of thousands of people would have a flying start.

"I think it would really excite people.

"You couldn't just have a write in candidacy. The National Executive of the Labour Party would have to agree, here are the following candidates to choose from.

"Everyone would pay a pound and sign a thing saying they support the Labour Party.

"I think you would get a lot of engagement. And in an era when people say politicians are cut off from the general public, you'd have Labour voters having a say in who the Labour candidate is. I think that would be a really exciting thing."

Blog The Chamberlain Files has reported that Labour only has 3,862 members in the city, potentially giving a small group of people a lot of control over who becomes mayor of Birmingham if the city does vote "yes" in a referendum on creating a directly elected mayor on May 3.

Previously, Ms Stuart has also urged her party to hold an open primary.

Mr Miliband is firmly in favour of mayors, as he explained in an interview with Will Green of the Newcastle Journal.

He said: ""We can't have a situation where the only name that's known in local government is Boris Johnson.

"Why should he be commanding the national stage? We need the elected leaders of our great cities to be commanding the national stage."