Novelist Robert Harris on uncovering the most scandalous secret love affair in British political history

For his latest bestseller, ‘Precipice’, Robert Harris trawled secret letters to bring to life the hidden relationship between prime minister HH Asquith and a beautiful young socialite more than three decades his junior. The author tells Geordie Greig about the female character who moved him to tears, what Asquith’s family really think of the book, and why contemporary British politics has been ‘a cloud’ over his seventh decade