Neither Miliband nor Balls is prime ministerial material

The news has been dominated by David Miliband's less-than-subtle pitch to oust Gordon Brown as premier. This has led to speculation over who could possibly challenge Miliband should Brown be ousted, with Ed Balls another early favourite.

During my six-year stint on Building, I interviewed both these young pretenders: Miliband when he was the education minister in charge of the £65bn programme to rebuild every school in the country and Balls when he was a newly elected backbencher. Previously, Balls was of course the main economic adviser to then-chancellor Brown, although most think that he has essentially retained the role ever since.

I have to say, I didn't feel that either of them was prime minister material.

Balls lacks a certain gravitas, which his often-stumbling media performances emphasise, while Miliband doesn't seem quite the genius his backers claim

Balls, while one of the most obviously intelligent people I've ever met (though in that late-2005 interview he incorrectly forecast that the housing market would remain steady then grow again), lacks the charisma for number 10.

This is not to say that he is not charming in person. He was extremely polite, witty and incredibly personable - and there is no doubt you would not worry if this man were in charge of a big spending department. But Balls lacks a certain gravitas, which his often-stumbling media performances emphasise. Tony Blair has immense charisma - and that's why people voted for him, love him or loathe him.

Miliband was a really friendly bloke, but he didn't seem to be quite the genius his backers, colleagues and even foes claim him to be. For instance, he couldn't grasp that people were not entering the construction industry, suggesting that he was poorly briefed and failed to perceive that society pushes its best and brightest into financial services, the law and, indeed, politics.

Not only could he fill a suit, Jon Cruddas was as likeable as Miliband and Balls and about as impressive intellectually

He is another who is occasionally awkward on the television. Miliband is also rather wiry looking. That sounds daft, but Alastair Campbell always insisted that Blair fill his suit so that there was a presence about him. I'm not sure that Miliband has that presence, with or without an extra few pounds.

A third person I interviewed at Building, and a man that has been described as a potential stalking horse, is Jon Cruddas.

Although not as strongly to the left as he has often been portrayed, the former deputy Labour leadership candidate's reputation for strong views probably rules him out in this centrist era. But not only could he fill a suit, Cruddas was as likeable as Miliband and Balls and about as impressive intellectually.

Brown should stay. Convention does not really suggest that two unelected prime ministers should be around in the same term of office

I doubt he'll stand, though. A source close to him told me that Cruddas isn't interested in even debating the whole situation until he returns from his holidays, and the suggestion was that Brown - and they are not friends - should probably stay.

I love the speculation that surrounds the prospect of a leadership change - but Brown should stay, in my view.

Only an incredibly tiny part of the UK constitution is codified; it is essentially based on convention. And convention does not really suggest that two unelected prime ministers should be around in the same term of office.

Nor would it be acceptable for a replacement to immediately call an election - people will want to see him or her lead for a little while, much like they examine the actions of David Cameron to decide his prospective worth as prime minister.

However, I fear that this will not blow over. Brown will go, leaving a constitutional crisis, and I very much doubt that Miliband or Balls will be the ones asked to pick up the pieces.