There are a lot of questionable stories about the diminutive, sparkly and very sociable historian Andrew Roberts. An ex-girlfriend claims he has framed pictures of Margaret Thatcher not just in his study and drawing room but also next to his bed. During his single days, he was supposed to rival Casanova with his successful romantic conquests. And there's a widespread belief among the denizens of social London that his wealth comes not from history but from a family interest in the British franchises of Kentucky Fried Chicken.

Then there are those who claim he is among the finest historians of his generation and will be one of the big thinkers behind the next Conservative government, pointing to his close acquaintance with David Cameron and old friendships with Michael Gove, Oliver Letwin and, more surprisingly, Cameron's touchy-feely strategy chief, Steve Hilton.

It is certainly the case that it is practically impossible to go to a smart party in London without finding Roberts, usually squiring a beautiful woman - recently his second wife, public relations executive, Susan Gilchrist - and always surrounded by admirers listening to his tales of cosy dinners with George Bush and Nicolas Sarkozy. Of the other rumours, the bedside photograph will have been banished since his marriage (though his admiration for Lady Thatcher is undiminished), his romantic prowess speaks for itself and the ownership of KFC is true, though the family money also comes from the sale of Job's Dairy in 1987, and his books sell a fair few copies.

As a historian, Roberts is facing a defining moment. Next week sees the publication of The Storm of War, subtitled with characteristic bravado: "A New History of the Second World War". It runs to well over 600 pages and may be his masterpiece, concentrating on Hitler's personality and his Nazism and providing an answer to the biggest question of all: why the Germans lost the war....