As historian David Burke points out, the basic requirement of any spy is not to look conspicuous. So when, between the mid-1930s and mid-1940s, around 25 Soviet operatives came to live next to each other in one of London’s new landmark modernist buildings, it didn’t sound like the smartest move.

If there was method to such madness, though, it was that no-one pays attention to the man living next door to Agatha Christie. The legendary crime novelist lived at Hampstead’s Lawn Road flats – also known as the Isokon building – from 1941 until 1947 and, as Burke says, was surely no stranger to its peculiar clientele.

“It would have been almost impossible not to know what was going on. The photos give you an impression of how close people were to each other; the Isobar was downstairs and you can see how cheek by jowl people would have been.

“Certainly her only spy novel N or M? was written here and is impressive for its knowledge of spy tradecraft and Fifth Column activity in wartime Britain. Where else would she get that knowledge from, when it’s such a far cry from a murder in a vicarage?”

The time spent by Christie in the Isokon is just one chapter of its incredible 80-year history, which is documented in Burke’s new book The Lawn Road Flats: Spies, Writers and Artists.

Designed in isometric drawings by pioneering architect Wells Coates, the building saw reinforced concrete being used in British domestic architecture for the first time and, consequently, it attracted a rich strain of artists sympathetic to the modernist cause.

Painter and sculptor Henry Moore, novelist Nicholas Monsarrat and Bauhaus exiles Walter Gropius, László Moholy-Nagy and Marcel Breuer were just some of the cultural elite who took shelter in its walls, but it was the presence of one Arnold Deutsch that first drew Burke’s attention.

This unassuming university lecturer was actually controller of the infamous “Cambridge Five” – a group of Cambridge university spies famously turned against Britain during the Second World War. A paragraph in Christopher Andrew and Vasali Mitrokhin’s The Mitrokhin Archive opened Burke’s eyes to this fact, but nothing prepared him for the discovery that not just one, but scores of spies lived within the Lawn Road flats – often at the same time.

“It is still, whatever way you look at it, just weird. For so many to live so close together, it goes against all the principles of the intelligence craft.

“All I can do is refer to something George Orwell once said: the English murderer keeps the corpse close by, while the American murderer puts as much distance between them as possible. I suppose, in some way, British and American spies were similar to their homicidal counterparts.”

Since its remarkable early days, the Isokon has experienced mixed fortunes. In 1969, the Isobar was also converted into flats and then, in 1972, the building was sold to Camden Council, before it gradually deteriorated to the point of abandonment. Following a refurbishment in 2003, however, it has now been declared a Grade I-listed building and its value is once again clear to see.

“The Isokon was built at a time when nobody was carrying around the same amount of baggage that they might have had in the 1920s,” says Burke. “It was minimalist and designed for those who didn’t want to have possessions, things that would tie them down. For lack of a better word, it was aimed at young professional people who wanted to, essentially, live.”

The Lawn Road Flats: Spies, Writers and Artists by David Burke is published by Boydell Press priced £25.