It’s 1960 and Bob and Barbara Jackson are living a quiet and contented suburban life with their teenage daughter Julie in Ruislip.

Their best friends are Peter and Helen Kroger, an outgoing Canadian couple who live across the road. Peter and Helen have bought Barbara an easel for her night school art classes, while Barbara is making an elaborate dress for Helen.

But when they are contacted by a mysterious Mr Stewart, the Jacksons’ never-had-it-so-good life begins to unravel. Stewart, part of some unspecified Government agency, wants access to a room where he and his colleagues can observe the comings and goings of a mysterious man who spends much of the weekend with the Krogers.

Based on the true story of Morris and Lona Cohen, who were arrested in 1961 as part of the Portland spy ring, Hugh Whitemore’s fascinating 1983 play evokes an era of seeming innocence when the Cold War could nevertheless surface suddenly like a nuclear submarine in a quiet London suburb.

As the official toe in the door turns into an extended residency, layers of deceit are revealed, from Peter and Helen’s fictional Canadian background to Bob and Barbara’s pretence that everything is normal. Betrayals range from one of the surveillance officers revealing that Julie is flouting a ban on riding her boyfriend’s motorcycle to the Soviet Union’s abuse of a generation of 1930s idealists.

Barbara, a staid middle-class housewife of a kind that is now the stuff of nostalgic parody, is the character who is most wounded by events, who clings to principles of loyalty when her baffled husband’s instinct is to conform uncomplainingly with authority.

This revival by Christopher Morahan is beautifully performed, particularly by Jenny Seagrove as Barbara and Lorna Luft as the ebullient Helen, an unlikely high-ranking officer in the KGB.

* Running time: Two hours, 15 minutes. Until Saturday.