It is one of the many myths of Australian history that the 1950s was a boring decade in which nothing much happened. Yet the 1950s remain in the news today – confirming that the theory is very much fiction.

Last week the National Archives in Britain released new material about Vladimir and Evdokia Petrov, who defected to Australia in 1954 while employed in the Soviet embassy in Canberra. Most of the details of what is termed the Petrov Affair are known – due to the wise decision of Bob Hawke’s Labor government to release the files held on the matter in the Australian Archives. This led to Robert Manne’s important book The Petrov Affair (1987).

In time, further archival material was released, including from the former Soviet Union after the collapse of European communism. This information is covered in David McKnight’s Australian Spies and their Secrets and Breaking the Codes by Desmond Ball and David Horner.

The release of the MI5 files adds two pieces of information to our knowledge. First, according to a top-secret cable, Sir Charles Spry, the director-general of ASIO, advised that, in the event of the Labor leader, Bert Evatt, becoming prime minister after the 1954 election, the British government should withhold important secrets from Australia.

In The Australian last Monday, both Manne and McKnight criticised Spry’s actions. Manne said that Spry had an allegiance “to some concept of a broader free world, not to the elected Australian government”. McKnight described Spry’s actions as “disturbing” and “a little scary”.

But was it? Spry knew then what we know now. Evatt was minister for external affairs from October 1941 to December 1949. During the second half of the 1940s, Josef Stalin’s Soviet Union infiltrated his department.

The USSR’s chief agent in Australia was Wally Clayton and his spies in the Department of External Affairs included Ric Throssell (the son of the communist writer Katharine Susannah Prichard), Ian Milner and Jim Hill. There were almost certainly more. Moreover, some members of Evatt’s staff were known to be in contact with the Soviet embassy. As Richard Hall documents in his book The Rhodes Scholar Spy , Milner defected to communist Czechoslovakia in 1951 during the height of the Stalinist purges in that country.

Mark Aarons, the son of long-time Communist Party of Australia functionary Laurie Aarons, is no right-winger. In his 2010 book The Family File, Aarons documents that the party received substantial funding from Moscow, that some members (but not his father) were Soviet agents and that some Labor parliamentarians, who were close to Evatt and the pro-communist left in the ALP at the time, held dual membership of the Communist Party and the ALP.

Moreover, Australia was no backwater but rather an important part of the Western alliance. That’s why the Soviet Union attempted, successfully as it turned out, to infiltrate the Australian public service and political parties.

And then there was the fact – as was widely known but unacknowledged at the time – that Evatt was suffering from a serious mental illness. This was evident in the 1940s and undeniable by the early 1960s. But it was a reality in the 1950s – when Evatt exhibited serious mood swings. As such, he could be a committed anti-communist on Monday and a Soviet apologist on Tuesday.

If Evatt had become prime minister in May 1954 he would almost certainly have sacked Spry. If not, Spry probably would have resigned as head of ASIO. The MI5 documents reveal that, in the midst of the Cold War, Spry was willing to put the interests of the West ahead of his own career. Also, he was not disloyal to any Australian government – if only because when Spry offered his advice to the British, Evatt was leader of the opposition.

The MI5 papers also contain a document indicating that, in the lead-up to the 1958 election, Robert Menzies ordered ASIO to hand over copies of top-secret documents concerning the Petrov affair to Britain and the US. The prime minister was concerned that if Evatt won the 1958 election he would order the destruction of the Petrov files held by ASIO. Since it is now acknowledged that Vladimir and Evdokia Petrov (who was an expert on codes) were among the most important Soviet defectors in the 1950s, Menzies’ decision also makes sense.

As it turned out, Evatt led Labor to defeats in 1954, 1955 and 1958 and left politics. So Spry and Menzies never had to put their plans into effect. That they acted in accordance with their perception of the national interest, and not for party political reasons, is evident from the fact that it took over half a century for their decisions to become public. And then the relevant documents were released by the British.