Jeremy Corbyn was “very useful” to the Soviet Union and he undermined British security, the International Trade Secretary has claimed.
Tory MP Ben Bradley was right to apologise for claiming the Labour leader “sold British secrets to Communist spies”, Liam Fox said.
But the Cabinet Minister said Labour’s left were “useful idiots” during the Cold War and acted in a way that was “damaging” to the country.
Mr Bradley tweeted an apology to Mr Corbyn and agreed to make a “substantial” donation to charity for a tweet making claims about his links to Cold War agents.
Mr Fox told BBC One’s The Andrew Marr Show: “If you say something that is untrue you have to say so,” he said.
Mr Fox distanced himself from comments made by Defence Secretary Gavin Williamson about the Labour leader, saying he would not have used the word “betray” about Mr Corbyn’s actions.
“I certainly think that the Labour left were the Soviet Union’s useful idiots during that period,” he added.
“I certainly believe and I think it is true that Jeremy Corbyn and others were very useful to the Soviet Union during the Cold War because they undermined the arguments of the West.
“I think in the broadest sense he was undermining the security of our country by siding with the Soviet Union in that argument and I think that was very damaging to the country.
“Luckily it was our side of the argument, not Jeremy Corbyn’s, that won the day.”
Mr Fox said: “It is very clear that Jeremy Corbyn and his fellow left wingers were undermining the case for our security.”
A series of newspaper stories have made allegations about Mr Corbyn’s contact with a Czech intelligence agent in the 1980s.
Jan Sarkocy, a former agent of the Czech StB intelligence agency, has been described as a fantasist by Mr Corbyn’s allies.
Mr Corbyn’s spokesman has previously challenged records of supposed meetings between the then Labour backbencher and Mr Sarkocy.
The Labour leader recalled speaking to a diplomat from the then communist country in 1986, as one of many meetings with ambassadors, politicians, activists and dissidents from “the majority of countries in the world”, said the spokesman.
But another meeting with the same man was recorded in StB files as taking place the following year in the House of Commons, on a Saturday when the Labour MP’s own diaries record he was attending a conference in Chesterfield.
A Labour party spokesman said: “Liam Fox should focus on his job and not give credence to claims that everyone knows are entirely false and ridiculous.”