At 45 Cranley Drive, Ruislip, in 1961, 2 Russian spies were arrested.  According to their friends and neighbours, they were Peter and Helen Kroger, from New Zealand.  And their passports were genuine.
But their fingerprints revealed them to be Morris and Leontina Cohen, from the US originally, communists from poor Polish Jewish families.  Morris had fought in the Spanish Civil War.
She had run a network of agents working in munition plants at the end of the war, she then became a courier for taking reports from the Los Alamos atomic weapons programme in New Mexico to New York.  When Julius Rosenberg was arrested (and later executed) for spying, they disappeared.  7 years later they returned to the USSR.
But they resurfaced a few years later in England.  When their house was finally raided, it was full of sophisticated radio equipment, and Helen had microdots in her handbag.  They consistently denied their true identities and were sentenced to 20 years in prison.
After 8 years, they were exchanged for a British subject who had been arrested for anti-Soviet activity.