Media playback is unsupported on your device Media caption Listen to a clip of Natalie Bennett's radio interview with Nick Ferrari on LBC

Natalie Bennett's "mind blank" on live radio derailed the Green Party's big policy launch. Can such moments end careers or should everyone just calm down?

Umm. Let me...ah.... I'm glad you asked me that....

It has happened to everyone - particularly in stressful situations such as a job interview, which is the nearest most of us will get to the sort of pressure politicians come under when being grilled live on air by an experienced broadcast journalist.

What makes LBC's Nick Ferrari interview so compelling is that he does not bully or hector Ms Bennett, he just keeps pushing the point quietly and relentlessly.

And the Green Party leader simply seems to crumble. Some of the silences are so big you could drive a bus through them, as she attempts to explain how the party would build 500,000 new homes on a budget of £27bn, although Ms Bennett mistakenly says £2.7bn, prompting a quizzical response from Ferrari (whose maths are also a bit suspect at this point).

That works out at £60,000 a house, "not much more than the cost of a large conservatory," says the LBC presenter, "how are you going to pay for the land?"

Long pause. "Right, well what we are looking at doing is... is... is basically," says Ms Bennett before having a coughing fit and explaining that she has a "huge cold".

Unforced error

Modern political journalism thrives on such moments. It busts through the spin matrix to reveal something real and human. And it makes for a great clip.

Image caption UKIP leader Lord Pearson was not a details man

Political leaders are meant to have the details at their fingertips at all times. Particularly if they are defending one of their own flagship policies. This is the job they have been elected to do.

Shadow chancellor Ed Balls had a case of "mind blank" on Newsnight recently, when he could not recall the surname of one of Labour's biggest business backers Bill Thomas.

This might fall into the category of an unforced error - it was Mr Balls who brought up "Bill Somebody" in the first place - and although he tried to laugh off his memory lapse, it furnished David Cameron with a snappy comedy line in the Commons: "Bill Somebody's not a person, Bill Somebody is Labour policy."

Media playback is unsupported on your device Media caption Ed Balls: "His surname has just gone from my head, which is a bit annoying"

Lord Pearson of Rannoch, who led UKIP into the 2010 general election, could not remember several UKIP policies in an interview with the BBC's Jon Sopel.

The insouciant Pearson - who stood down as UKIP leader shortly after the election admitting he was not really cut out for the demands of frontline politics - insisted he had read the party's manifesto but he was not a details man. He was more interested in the "broad sweep" of policy.

'Excruciating'

But for brain freeze of the purest kind, you have to turn to the US and the 2012 race for the Republican nomination.

One fancied contender, Texas governor Rick Perry decided, in a live TV debate, to list the three government departments he would axe if he made it to the White House. The trouble is, he could only remember two of them. And that was that for Perry's presidential bid.

Natalie Bennett was quick to apologise to party members and supporters for her "excruciating mental brain fade". It might even garner some sympathy from Green supporters, who like to think they are more human and caring than the rest.

Media playback is unsupported on your device Media caption Footage courtesy of MSNBC

Bennett is relatively new to front-line politics and, like UKIP in 2010 and again this year, her party is being subjected to a level of scrutiny it does not normally get because it is gaining support in the polls.

The danger for the Greens is that the kind of floating voter the party is trying to attract from Labour and the Lib Dems will be left with an impression of incompetence or of a party leader that is not up to the job. There are other clips of her struggling to answer questions from journalists.

But maybe potential Green voters will not care - they know the party is highly unlikely to form the next government and that they are trying to do something different in an often hostile media environment.

UKIP has, arguably, made worse gaffes and has continued to prosper in the polls.

What is certain is that the audio clip of Bennett's interview will live on online, ready to be used again the next time a politician stops in mid-sentence and feels the ground beneath them open up.