Il labirinto

But Sebba makes a convincing case that what occurred with Randolph was a coup de foudre - however unlikely that may seem given how Randolph looked and behaved. She is equally persuasive that Winston was most probably conceived before they married, in 1874 - attesting to Jennie's 'confidence, physical passion, craving for excitement and sexual fearlessness' - though the author's plea that her interest here is 'not a prurient one' sounds a little priggish.

Overall, however, Sebba's tone is far from that; her prose is clear, her judgments sensible. She is good on how Jennie helped the erratic Randolph in his strangely meteoric political career and moving when chronicling the disintegration of their marriage and their final world cruise as he went through what were probably the last stages of syphilis - Rosebery memorably recorded that Randolph was 'the chief mourner at his own protracted funeral'. But the real strength of the book is its examination of Jennie's role in shaping the character and career of Winston.

It is hard to disagree with the assessment of Winston's daughter Mary Soames that even by the standards of their generation, Lord and Lady Randolph Churchill were 'pretty awful parents' to their eldest son when he was a boy.

This book has plenty of evidence to back this up - notably Winston's letters from his peculiarly sadistic prep school imploring his parents to take him away, or at least come and see him; on the back of some of these are scribbled the names of those Jennie planned to ask to dinner. Sebba does not deny the neglect, but nevertheless has us believe that Jennie always loved her eldest son, and that she 'always knew that Winston would be her greatest achievement'.

Winston's adolescent letters accusing his mother of maltreatment, far from damaging their relationship, taught him 'how far he could push and still carry those who loved and supported him, basic leadership skills', writes Sebba.

When he was ready to embark on a career, Jennie badgered everyone she thought might advance it. His pushy mother made Churchill a controversial figure at times, but no one could say that she hadn't helped him on his way.

Sebba suggests that Jennie's liking for younger men - her second husband, George Cornwallis-West, was, like her third, more than 20 years her junior - was due to the fact that she did not wish to allow anyone to compete with Winston for her attention. And she never did. She even interrupted her honeymoon with Cornwallis-West to help her son's election campaign in Oldham.