‘I will never forget his kiss’, the Princess Marthe Bibesco wrote in 1933, ‘so young, so strangely chaste, insistent, searching my lips and sealing them with his ... a moment we both felt had been long in coming.’ The words smack of the bodice rippers she churned out, when times were hard, under the pseudonym Lucile Ducaux. They far outsold the impressive, cultish volumes she wrote under her own name, earning her the admiration of the Académie Française and causing Proust to acclaim her as one of the greatest stylists in French prose.

The words, however, belong not to fiction but to her diary. The climactic kiss took place not in the pages of the French equivalent of Mills & Boon, but in 10 Downing Street. ‘He’ was Ramsay MacDonald, then nearly seventy. Bibesco’s considerable