THE HISTORIAN, by common perception, is not a profession for the louche or the fast-living. The image that most quickly comes to mind is of Robert Newman and David Baddiel's two elderly buffers in their sketch 'History Today', cobwebbed in dandruff, limbs creaking, furiously arguing over the principal cause of the Franco-Prussian war of 1870, but still intent on hurling schoolyard insults such as: "See that mouldy old sandwich? That's you, that is."
So, if Newman and Baddiel were the ones who helped to hammer shut the coffin lid on a career in history, Andrew Roberts must surely be credited for animating the undead. Of course, the author does that each day: blowing life into figures long dead and placing the reader in the room as they wreak destruction (Hitler in The Storm of War) or save the western world from a bunker in London (Churchill in Masters and Commanders).
In many ways, Andrew Roberts, small, polite and impeccably dressed, is the James Bond of contemporary historians: always popping into Number 10 Downing Street or lunching at the White House. No peer could better animate a class of surly teenagers to follow his lead than Roberts could, simply by describing his working day. Sure, he may rise at 5am and work steadily until 6pm, with a 45-minute nap mid-afternoon, but cometh the cocktail hour, cometh the man as no-one attends more parties, dinners or soires. The mantelpiece of his London home positively groans under the "stiffies", although, as he explains, publishers are cutting back: "At this time of year I'd usually have 60 invitations; it must be down to 40."
Yet spend some time in his company and it's little wonder the invitations keep on popping through the letterbox. He's funny, charming and considerate, so when he begins to explain how misunderstood George W Bush is, you almost believe him. So impeccable is this historian's connections that he has a framed photograph of that former leader of the United States handing a copy of his book, A History of the English-Speaking Peoples Since 1900, to Tony Blair.
Sitting in the bar of the Balmoral Hotel in Edinburgh, he laughs when I bring it up. We're both sipping orange juice, as it's 8am. Roberts is in town to visit his two children from his first marriage and has a later appointment to lecture at a finance house on leadership in difficult times. We agree it's appropriate.
"Yes – the photograph – how funny," he says. It had been mentioned in a recent profile of Roberts and his new wife, Susan Gilchrist, in Tatler magazine. "The President had received a copy of the book and sent me a charming handwritten note saying how much he had enjoyed it and suggesting I give him a call next time I was in Washington. He had included his personal line at the Oval Office – of course, I arranged to be in America shortly afterwards and, as good as his word, he invited Susan and I to visit him. We had 45 minutes alone in the Oval Office followed by lunch with him and Dick Cheney.
"He does read a great deal. When he was last in London he asked for a dinner with historians and when I was chatting to everyone afterwards they all felt he had indeed read the books."
The visit to Washington led to a notorious diary piece he wrote for the Spectator magazine that dwarfed all previous attempts at name-dropping, with every world leader he encountered, including President Sarkozy, praising his work. Still, who could blame them? Roberts writes historical prose like few others. He clearly marshals the material and is brilliant at illuminating a character with a telling anecdote.
For the past three years he has been re-living the Second World War for two massive tomes, published by Allen Lane. Last August Masters and Commanders crashed down onto my desk, 673 pages, in which he told the beguiling story of how Roosevelt, Churchill and their respective military commanders, General George C Marshall and General Sir Alan Brook, won the war in the west. Widely reviewed as his masterpiece it was surprising to see it followed up less than 11 months later by The Storm of War: A New History of the Second World War, all 680 pages of it. In all honesty, I suspected a swift cuttings job – how else could it possibly have been created? – but, instead, it's a gem of compression that swerves round the old stories and furnishes a fresh take on the old campaigns.
How did he do it? "Well, the secret was researching the two books at once. Whenever I was visiting all the different archives, I would invariably come across material that best suited one book or the other and I would file it away. I'm very proud that there is not a single sentence, argument or overlap or quote that appears in both books. Every piece of information either went into one book or another."
Once the research was complete he could rely on the fact that he is an exceedingly quick writer. Authors who assuage their guilt with the knowledge that Graham Greene considered 250 words to be a profitable day should look away now: on an average day Roberts can power through 8,000 words. And this is writing – not, as Truman Capote said dismissively of Jack Kerouac, "typing".
"I'm quite lucky with my aunt's farmhouse in the Dordogne. It's very simple with no television or phones, or a swimming pool – no distractions at all – and I go over there for four weeks and all I do, apart from one quick phone call each night to Susan, is write. It's amazing how much you can get done. It was the ideal working environment and I managed to write 350,000 words in six weeks. All I did was work and sleep."
Both books are flavoured by visits Roberts made to all the battlefields. "Yes, I was very lucky that my wife is so wonderful and understanding. Even on our honeymoon she accompanied me to the Kanchanaburi death camp on the River Kwai."
Perhaps the most devastating chapter deals with the Final Solution and it is a mini-masterpiece of restraint. There is no judgment or sermonising, just devastating fact laid upon fact, building into a wall that briefly separates the reader from mankind. "I wrote it just after a visit to Auschwitz-Birkenau and our Polish guide played it exactly that way, with no emotion or need for sentimentality. The emotion wells up naturally from what you see – the mountain of hair, the vast piles of shoes, the suitcases. It does not require adverbs."
Last year rumours drifted along that GW Bush was keen to appoint Roberts as his official biographer. "I don't know how it started, but it's something I would be very interested in considering, although it would be unusual for a non-American to get the job." Still, he remains close to the family, writing in his most recent diary for the Spectator about lunching – then also dining – with George HW Bush at the family's home on Kennebunkport.
He had previously, through his friendship with Henry Kissinger, been offered the job of writing his official biography, but faced with the 30 tons of material in the former secretary of state's archive and his reluctance to employ researchers – preferring to sift himself – he passed it by.
Niall Ferguson has now taken the job. "Niall is a tenured professor and has a team of researchers – he's also, and I'm the first to admit it, far, far cleverer than I am and will do a wonderful job."
Yet for Roberts the war is over. He is leaving behind the misery of the Second World War to which he has devoted so many years of his life and is, instead, now hard at work on a massive biography of Napoleon.
"It's a huge cradle-to-the-grave account and I'm planning to visit all the major battlefields and, of course, St Helena where he died. But the only problem is that it's a bugger to get there. It takes a week to sail there and you could probably see round the whole island in an afternoon. Susan, I'm afraid, will not be joining me on this one."
• The Storm of War: A New History of the Second World War is published by Allen Lane, priced 25. Andrew Roberts will be speaking at the Edinburgh Book Festival on Monday, 31 August at 2 pm.