Robert Elms has written about one of London's most successful – and most forgotten – mass murderers

As a result, some of the tales come directly from his own life, and near misses with fateful tragedies: there’s London’s most successful, and least remembered, mass murderer, John Thompson, who killed 37 people in a night when he set fire to the Spanish Rooms club in St Giles. He is one of the most prolific mass killers in British history, earned the name in 1980 and yet, as Elms says, is “a notorious man with no notoriety". Equally – though it only gets a postscript in the book – a mention of John Christie, the serial killer who murdered his tenants at 10 Rillington Place and almost secured Robert’s parents for one of his rooms. “I remember my mum saying to me, 'Oh, he was quite a jolly chap, but your dad said there's something a bit creepy about him,’” recalls Elms. He’s been collecting anecdotes for this book for years in a large leather volume, so there's no doubt some quality ones never reached the page: one, about a transvestite bank robber caught in Hampstead Tube station, now lies on the cutting room floor.

Robert Elms has written about one of London's most successful – and most forgotten – mass murderers

Other sections are filled with incidents that are unique to Elms after decades living around London, from Burnt Oak to Holborn to Camden. There’s the incident when money rains from the sky near the soon-to-be British Library, or the story of the monkey jazz band in Notting Dale, “a troupe of 13 simian swingers to entertain the happy flappers” who escaped their captivity, some of them ending up as far away as Rugby. In Camden, the tone moves from pantomime to paean: even for someone who has never lived in North London, the way he writes about the bars of his neighbourhood fills one with a – to use a word he mentions in the book – "saudade", “a longing for your former land”. Except often, both for Elms and for me, the longing is for a place you can’t go back to, and maybe never visited.

The book, in many ways, is based around its opening line from Elms’ late mother: “This is no longer my London.” To Elms, what is fascinating is how everybody’s version of the city only lives as long as they do. Similarly, his mother’s declaration that Notting Hill – even post-Richard Curtis – is a “slum” means that this particular term, used equally as criticism, technical definition and compliment, occurs frequently in every chapter. “The young need slums,” says Elms, who writes vividly of his squatting years in the book. “What you require above all else is somewhere cheap and ideally central enough that you can take advantage of the capital.”

“I think that's one of the great dangers for London,” he adds. “Affluence likes to stay the same, because you're doing quite well, thank you very much, whereas poverty likes to change, and it gives cities an energy.”