As Robert Harris demonstrated in his superb trilogy about the Roman statesman Cicero — “Imperium” (2006), “Conspirata” (2009) and “Dictator” (2015) — he is a master of the political novel. In his new book, Precipice, a tale of infatuation and detection set in England at the outset of World War I, Harris again embellishes the record to accentuate the drama — and, in this case, the comedy, too — that historians often miss

Yes, this is a political novel, but it is also a love story, or perhaps one should say the story of an infatuation. 1914 when the book begins, Asquith had been Prime Minister for six years. There were difficulties, chiefly the acute Irish Problem, but he was serenely master of his cabinet. He was inclined to drink too much brandy in the evening, but his ability to transact business was unquestionable. He was 60 and married with seven children, five from his first marriage and two from his second to Margot Tennant. Asquith came from a middle-class Yorkshire family but moved comfortably among the aristocracy. He was at ease with women and enjoyed their company. Now, in 1914, he was in love

The young woman was Venetia Stanley, 26, daughter of the wealthy Lord Sheffield, from childhood a close friend of Asquith’s daughter Violet, and member of a group of playboys and playgirls known as the Coterie. The state of the nation transformed what might have been merely a breach of propriety into an affair to remember. Asquith was prime minister when the Great War broke out in the summer of 1914, and Stanley became his confidante and secret adviser during his final year and a half in office

Asquith was smitten, and Venetia was flattered; she was also very fond of him. He was “Darling Mr Asquith”. He took her for drives in his chauffeur-driven car, the partition between the front and back seats closed, and wrote letters to her every day, sometimes more than once. The Post Office was remarkably efficient then – a letter posted at lunchtime might be delivered in the late afternoon post. His letters were loving, gossipy and indiscreet. All his letters quoted in the novel are, Harris tells us, authentic – “the reader may be astonished to learn”. Quite so. Venetia’s, in reply, are invented by the author

Stanley, considered “handsome rather than beautiful,” was endowed with a keen intellect and a restless curiosity that soon made her invaluable to her confider. In the acknowledgements, Harris argues that “it strains credulity to [the] breaking point … to suggest … that the affair was not, at least in some sense, physical.” But their correspondence may have mattered more than the sex

Asquith is a shrewd but cautious politician, loath to make decisions until he absolutely must. With as many as a dozen mail deliveries per day, letters come and go at near-telegraphic speed, so if Asquith’s schedule is too tight for a personal consultation with Stanley, he may have time to lay out an issue for her on paper and get the benefit of her advice before acting. Often, her suggestions track with what he was already inclined to do, but at any rate, he can count on her to speak her mind frankly and without ulterior motives. “There was no such a thing in politics as true friendship,” Harris writes. “There could never be absolute trust, not when one was Prime Minister. … Only with Venetia was [Asquith] completely unguarded”

The assassination of Archduke Franz Ferdinand and Austria’s bellicose ultimatum to Serbia leaves Asquith and his advisers poleaxed, but they can’t stay that way very long — the duty of preparing England for a war likely to draw in Germany, Russia and France at the very least, is too pressing. Dominating those meetings as the war heats up is the first lord of the admiralty, Winston Churchill. Harris’s sketch of the young Winston is brilliant and any reader with a passing knowledge of World War I will cringe as Churchill continues to champion hopeless British attacks on the heavily fortified Turkish positions along the Dardanelles and the Gallipoli Peninsula while Asquith tries to rein him in

As things in Europe escalate, the Prime Minister becomes increasingly out of his depth. Isolated and desperately in love, Asquith diverts himself from the constant demands of state with his relationship with Stanley. He writes to her several times daily, sharing diplomatic and military secrets. On their drives, he shows her the originals of top-secret papers, recklessly crumpling and tossing them out of his moving limousine like so much rubbish. Inevitably, the discards come to the attention of Special Branch, the British intelligence agency. Harris embellishes his fictionalised history with a made-up character: Paul Deemer, a bright young Metropolitan Police officer, who is detailed to the branch to help with what might be called “The Adventure of the Amorous Litterbug.” The Asquith-Stanley affair is a poorly kept secret, and Venetia’s name doesn’t take long to go on Deemer’s persons-of-interest list. A type of love triangle develops as Deemer reads their correspondence and becomes increasingly invested in their relationship, a fixation that has far-reaching consequences for everyone involved

Harris deploys his plot with the dexterity one has grown to expect from him. He blends war, news, politics, arguments about strategy, and his characters’ daily lives together deftly. Asquith left detail to the service chiefs; he was there, in his view, to be consulted, to advise and warn. His reluctance to upset the routine of his life was remarkable, though often sensible; he still took weekends in the country, found time for golf, and played bridge most evenings. But as Venetia chafed under the weight of his neediness and took nursing work in a hospital (which he insisted on visiting), she began to seek a way out. You can’t blame her, but it was a hard knock for Asquith, and his state of mind (and heart) contributed to the collapse of his government and loss of office

Robert Harris is, without doubt, a master of the historical fiction genre and has created a compelling narrative that brings to life a little-known historical event that had far-reaching consequences for British political history. Just how distracted with Venetia was Asquith in the run-up to the First World War, during the scandalous shell shortage, when the decision to launch the Gallipoli Campaign was forced through by Churchill, and with his own and his government’s gradually weakening position? Could Asquith, famed for his sharp forensic mind, have been able to change the course of events if he hadn’t been gripped by a ‘kind of madness’? Sadly, we will never know