Commander Mansfield Cummings, founding father of the Secret Service, has at last received his Blue Plaque. It was unveiled Monday 30 March, with your correspondent in attendance, not, as I had anticipated at the site of the Cummings’ 1923 death – corner of Melbury Road and Addison Road, W14 – but the site of the first proper SIS office and workshop on top of the National Liberal Office, aka Horse Guards Hotel.

Who is the best-selling writer in history after Shakespeare and the Bible? The answer is Agatha Christie who was born in Devon in 1890 but whose stories often feature London and who wrote what is the capital’s (and the world’s) longest-running play The Mousetrap, which is still playing at Saint Martin’s theatre sixty-five years after it opened. One of the original cast was the late Sir Richard Attenborough, who was paid partly with a share of rights from the play. These were never expected to be worth much but later in his career he was able to sell them to help finance his film about the life of Mahatma Gandhi starring Sir Ben Kingsley.