A British scientist who won a Nobel prize for his pioneering work on the DNA double helix was investigated by MI5 as a possible atom spy who had passed US nuclear secrets to the Russians.

The security service files released today at the National Archives show that New Zealand-born Professor Maurice Wilkins had worked during the second world war on the Manhattan Project, building the hydrogen bomb at Los Alamos, New Mexico.

In 1951, the FBI told MI5 that one of the nine Australian and New Zealand scientists had been in close contact with members of the American Communist party.

Wilkins was put under surveillance, with his post opened and movements tracked. But the only evidence against him was from a junior MI5 officer who had been with Wilkins at St Andrews University when the first of the atom spies, Dr Allan Nunn May, had been uncovered in 1946. Wilkins had known May personally and defended his action as justifiable.

The investigation was dropped in 1953 when his colleagues insisted that any leftwing sympathies had disappeared. "He comes to the college every morning with a copy of the the Times, which he has apparently read on the journey," said MI5's informant.