As a former territory of the British Empire and now a member of the 53-state Commonwealth of Nations, Australia has been visited multiple times by the members of the British royal family. But one such visit in the '70s is most memorable to an ex-New South Wales cop as it was the setting of the Lithgow Plot, a plot to assassinate the visiting royals at that time, Queen Elizabeth II and Prince Philip.

According to the late former Detective Superintendent Cliff McHardy, the plot to kill the Queen and Prince Philip happened when the couple visited Australia in 1970. On April 29 of that year, the couple was on board the Commissioner's Train traveling from Sydney to the town of Orange.

As the locomotive neared the Blue Mountains town of Lithgow, however, the train struck a large log wedged across the rails. While the train safely halted to a stop 200 meters from where it hit the log, the late McHardy said that it would have been catastrophic.

“If the train had reached its normal speed it would have plunged off the tracks and into an embankment,” the late McHardy revealed in 2009, almost four decades after the incident. What saved Queen Elizabeth II and Prince Philip was that the log was stuck under the trains’ front wheels and did not derail the locomotive.

Back then, it was not revealed that there was an attempt to take the Queen and the Prince Consort’s lives. McHardy said that investigating police were instructed to keep the detail quiet to avoid embarrassment to the host country, Australia.

However, the late McHardy insisted that it was an assassination attempt. “"My investigations showed that the log was deliberately placed on the tracks,” the ex-NSW cop explained. “They said keep it out of the press because the Queen is still out here and if it had broken the next morning there would have been all sorts of trouble and we can do without that in a small country town.”

But the gag order negatively affected police investigation. “We never came up with any decent suspects because if we interviewed people we seemed to be talking in riddles,” McHardy complained. “We couldn't disclose what our inquiries were about. Perhaps now that the story has gone public someone might come forward.”

When McHardy revealed the story in 2009, the New South Wales Police spokesman commented that it’s hard to determine the story’s validity. Meanwhile, Buckingham Palace also declined to comment on the alleged plot.

Queen Elizabeth and Prince Philip Queen Elizabeth II, Prince Philip, Duke of Edinburgh, make their way in the royal procession during day 1 of Royal Ascot at Ascot Racecourse. Charlie Crowhurst/Getty Images for Ascot Racecourse