(CNN)The two police officers trailed the university professor as he left his home in the southwest London suburbs and walked to the local railway station.
His name was Eric Burhop. An Australian immigrant who had become one of the United Kingdom's leading nuclear and theoretical physicists, he was also a former member of the team that built the first atomic bomb, a prominent peace campaigner, and the subject of surveillance by security services on at least three continents in the 1950s.
Tall and well built, with thinning hair and a ruddy complexion, Burhop walked "with a slight stoop and takes noticeably short strides," a later report noted. "He usually carries a small brown attache case and raincoat. Wears herring-bone tweed sports coats and grey flannels, brown shoes."
The officers, members of the UK's national security-focused Special Branch, followed as Burhop took the train to London's Waterloo station, where he was joined by a man of "medium build, oval face, clean shaven, tanned complexion," with whom he proceeded to University College London.
They watched Burhop all day, as he went about his academic duties, had lunch in the university canteen, visited a local bank, and bought the evening newspaper. Due to the size of the campus, they missed him going home for the evening, expressing frustration in a report that they had "insufficient personnel available to cover all the exits."
In addition to the close surveillance of Burhop's activities -- one unlucky officer sat and watched him plant flowers in the garden of his house for several hours -- documents show his letters and telegrams were intercepted, his phone was tapped, and his friends and acquaintances investigated.
The surveillance, and a growing suspicion by the UK authorities that he had at least at one point been a spy for the Soviet Union, is documented in newly discovered files in the British archives.
"This is a curious case of an (alleged spy) who was allowed to hide in plain sight in London," said Susanne Roff, a UK-based researcher of nuclear history. Roff discovered the files in the British archives while researching the UK's nuclear tests in Australia.
Burhop died in 1980. The documents show he was never brought in for questioning by the British security services, nor was he arrested for his alleged spying. He may have been unaware that he was under surveillance at all.
His story touches on the deep paranoia in the early decades of the Cold War, and the numerous intelligence failures by the British security services who, on discovering another alleged spy within their jurisdiction -- following multiple embarrassing defections -- appear to have decided it was easier to leave him be rather than draw attention to their own potential failings.
CNN has reviewed the documents provided by Roff, as well as additional -- since declassified -- secret surveillance records on Burhop found by CNN in the British and Australian archives. Two independent academics also reviewed the documents on CNN's request. Their conclusions are presented below.
In a statement, Burhop's children pointed out that he was never publicly accused of being a spy for the Soviet Union or any other country, nor charged with any crime. They expressed concern that this article would mar the memory of "a hugely respected man of the highest integrity" who devoted his life to science and peace.
"He was a man of peace who worked tirelessly towards a nuclear bomb-free world," the statement said. "(We) would hate to see all that he achieved being hugely diminished by suggestions that he was a spy."