The papers released by the National Archives recorded how Wilson fretted about being spied on by Soviet forces disguised as trawlers while he was bird-watching at his cottage off Cornwall in 1974.
Wilson won four general elections as Labor leader, two between 1964 and 1970 and two in 1974. He resigned as prime minister in March 1976 and died in 1995.
Ministry of Defense documents show Wilson was assured he was not being watched and others show he began suspecting members of Britain's MI5 domestic intelligence agency were plotting against him.
His press secretary, Joe Haines, told the BBC he recalled Wilson's fears.
"He gradually began to suspect everybody," Haines said. "He suspected MI5, he feared a military coup, he thought the Soviets or anybody else might be spying on him and it got worse and worse I'm afraid."