In her preface to this vivid and enjoyable rollercoaster of a book, Mary S Lovell pre-empts critics who may take her to task for adopting a gossipy tone by pleading guilty. She is right to make a virtue of reality as there is much in this family saga, told with elan and panache to the last of its almost 600 pages, to gossip about. From syphilis to gambling debts, alcoholism to papal annulments, it’s all here. Several of her protagonists indulge in innumerable adulterous affairs and marry three or even four times. There is also, along with the triumphs and romances, much tragedy and sadness, including suicides and nervous breakdowns, and the same stories could have been told with an air of gloom or moral censoriousness. Lovell does not go in for any of that. For example, Pamela Churchill, Winston’s much loved daughter-in-law married to Randolph and mother of little Winston, who comes a close second to the long suffering Clementine as the heroine of the book, is we are told often out of the country in the immediate aftermath of the War because of her busy social life and frequent visits to the USA. This, according to Lovell, had its benefits since the child often went to stay at Chartwell or Minterne so that both sets of grandparents saw a good deal of him – while she saw a good deal of Averill Harriman. “Pam, having enjoyed an amusing flirtation with David Niven …was now involved in a casual affair with the devastatingly handsome Prince Aly Khan,” Lovell writes briskly a few pages later.

Of course Winston himself towers over the whole clan, as he towers over the book. Yet, although there are already thousands of books about Winston, what Lovell succeeds in doing in this ambitious and original undertaking is putting him at the centre of a domestic setting, pitting the grave political demands against those of his family, equally relentless and in some ways more challenging.

Many of the stories she tells are not new but seeing how they impact on Winston as he bestrides the world stage adds immeasurably to their dramatic edge. Winston in 1935 was facing what Lovell describes as “Clementine’s only extra marital romance” – albeit non physical – with Terence Philip with whom she had gone cruising on Lord Moyne’s yacht, the divorce of his daughter Diana and her subsequent marriage to Duncan Sandys, the public espousal of communism by his nephew Esmond Romilly and finally, his favourite daughter Sarah announcing that she was going to marry the Viennese Jewish actor, Vic Oliver, whom Churchill viewed as an “itinerant vagabond.” Yet he was increasingly concerned about events in Europe and made his views known.

But the climax of the book is the moment when Winston, in May, 1940, is finally summoned aged 65 to be Prime Minister and writes in his diary of his profound sense that he was walking with destiny, a belief instilled in him by his American mother, Jennie. In December 1941 Winston travelled to Washington to deliver one of the most crucial speeches in his career and reflected on the accident of birth whereby his father was British and his mother American; what if it had been the other way around? He emphasised his ties of blood to American soil in order to persuade the USA to join in the war. Yet, however well known that speech to Congress, what is less known is how, hours beforehand, while still composing it he found time to see his nephew’s young wife, Decca Mitford with her ten month old daughter, and to tell her that Esmond – previously posted as missing – was almost certainly dead. He handed her an envelope with $500 dollars in it but she left screaming furiously and crying at the same time.

Lovell charts the rise of the Churchill dynasty from the first Duke and Duchess of Marlborough through to the present 11th Duke and his fourth duchess. But Winston and Clementine’s own family is the psychological heart of this well paced book with its large cast of characters. Winston’s adoring relationship with his only son, the handsome and charming Randolph, is central to the drama and painful to read. Clementine had periods when she was not on speaking terms with Randolph. Sister Mary said he was so difficult on occasions he would pick an argument with a chair. Yet Winston, determined to do better than his own abusive and absent father, could never bear to criticise Randolph. When he discovered the boy had been sexually abused at school he was angrier than his children had ever seen him before. Winston, ever forgiving towards Randolph, also protected him as an adult in wartime by telling army chiefs that if Randolph were killed he would not be able to continue as Prime Minister. In 1939, one of his first acts on assuming office as First Lord of the Admiralty was bringing the Duke and Duchess of Windsor back from France on HMS Kelly. He summoned Randolph to take part in the secret mission.

For whatever reason, his children – with the exception of the youngest, Mary now Lady Soames – endured periods of desperate unhappiness. Diana after her second marriage to Duncan Sandys finally collapsed, (she had put up with multiple infidelities), took her own life. Sarah became a “fully fledged alcoholic”, was arrested more than once with drying out periods in clinics and married three times while Randolph, after two failed marriages fell in love with a woman he could not marry. Lovell has unearthed many fascinating details about life in the Churchill family; bringing them all together reveals that, while calling on the nation for every last ounce of effort, Winston himself was being personally drained.