As markets crashed and the financial world lurched once more, Gordon Brown used a surprise appearance at The Times Cheltenham Literature Festival to argue that years of experience make him the only man to lead the country out of the crisis.

I interviewed the Prime Minister for an hour yesterday, in what was supposed to be a discussion of his new book about wartime heroes, but which swiftly became a tutorial on the economic emergency, and his role in the efforts to solve it. Even so, the event had a distinctly military theme.

A book festival may seem an unlikely place to find a man in the eye of a political and economic storm, but Mr Brown was determined that our conversation should focus on economic rather than literary matters.

The audience of A-level politics students, local VIPs and members of the public had not been told the identity of the guest at the “special opening event”, and gave an audible gasp as the Prime Minister took the stage in Cheltenham’s Victorian town hall.

Mr Brown brought with him reinforcements, referring to Picasso and General Sir William Slim of Burma, among others, to underline his leadership credentials.

The ageing Picasso, he recalled, once responded to a suggestion that his 45-second doodle was worth a fortune by saying: “It didn’t take me 45 seconds, it took me 82 years.”

“I just hope the experience I’ve gained over the last ten years is going to be of use to people in dealing with this particular set of problems now,” Mr Brown said.

In response, I recruited a French general to explore how Mr Brown has taken to his new role as leader of the battle against global financial meltdown.

“During the Battle of the Marne in 1914, Marshal Foch sent a report to headquarters that read: ‘My centre is giving way. My right is retreating. Situation excellent. I shall attack.’ Do you feel like that Prime Minister?” I asked.

There was a pause, and then a broad grin. There are explosions going off all over the financial world, but Mr Brown is advancing, and every syllable of his body language proclaimed that he is in his element.

Our on-stage interview had been planned as a discussion of his book, Wartime Courage: Stories of Extraordinary Courage by Ordinary Men and Women in World War Two. He apologised that, through force of circumstances, a literary chat would also be a lesson on how oil price rises and the credit crunch had led the world to financial mayhem.

The events of the past few weeks have changed the political dynamic, and Mr Brown is a changed man. Yesterday he was amusing, expansive and animated. If one did not know that he was facing the biggest financial crisis since the 1930s, potential calamity and political Armageddon, you could be forgiven for imagining that he was enjoying himself.

Mr Brown is at his worst in the political trenches, having mud thrown at him by friend and foe. He is at his best leading a charge across open ground.

He is at home with books; he may be the most bookish Prime Minister since Churchill. In some ways, he seems more comfortable with books than with people.

He is also fascinated by wartime bravery: this is a book he has been writing, on and off, for ten years. “The book is being published now, but I wrote it some time ago. I have been busy on the issues of the day.”

It is about ordinary people finding courage in extraordinary circumstances, about inner resources and moral strength, and about leadership. There is little doubt that in the present crisis, Mr Brown has also found a battlefield he understands, terrain he believes he can negotiate.

Bill Clinton, I pointed out, always felt that his time in office lacked a “real crisis”, a defining challenge through which he could demonstrate his presidential mettle. I asked Mr Brown if he felt that this was his defining crisis, his moment. Again the pause, and the grin; he rolled his eyes, and changed the subject.

Mr Brown is too canny to admit that adversity suits him, or to predict that the war is being won. As Churchill said in November 1942: “Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.” There will be blood, sweat and tears to come, and all three are likely to be shed by Mr Brown in the coming months.

“I can’t predict what’s going to happen in the next few months. I know we have taken decisive action and I want other countries to follow us,” he said.

In his book, Mr Brown writes of the “happy warriors” in the Second World War who carried the fight against almost impossible odds.

Gordon Brown looked physically exhausted yesterday, anxious to show that he is fully focused on the global financial meltdown, and wary of overconfidence; yet he also seemed, in a way that I have never seen before, happy.

Markets diving. Credit evaporating. Shares crashing. Situation excellent. I shall attack.

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