Heinz Koch, who was in charge of the now defunct air carrier’s operations in Tehran at the time, said Swissair was not told about the true identities of the “very important Canadian passengers” until months after it carried the six US diplomats to safety aboard one of its airplanes.

“I was informed by the Canadian embassy that they have on this particular day very important Canadian passengers on board and we should make sure that they were not off-loaded last minute. But this was purely a reservation question, we had no direct impact on immigration,” he told World Radio Switzerland.

“It was a few months later when we got the first information that probably these US diplomats were on board this particular Swissair flight. But we made sure that this information didn’t pass around the world,” Koch said.

“We still wanted to operate to and from Tehran and it would have been a big risk if the authorities would have known that we were involved in this operation,” he added.

“Argo” stormed to Best Picture victory at the Oscars in Los Angeles. The honours for the Iran hostage drama marked a triumphant comeback into Hollywood’s mainstream for director Ben Affleck.

The thriller, based on a true story, recounts a CIA mission to rescue six American diplomats from Iran under the cover of making a fake Hollywood film. The six escape using falsified Canadian passports and the CIA role only emerged years later.

Iran’s culture minister Mohammad Hosseini said on Monday in a news agency report that the film was “anti-Iran” and lacked artistry.

Life in Tehran after the revolution – during which 52 American diplomats were held hostage — was tense, Koch said.

“The situation in town was very critical. Most other foreigners had left the country, especially families with school children because the international schools were closed down after the revolution.”

Travellers had to pass through many checkpoints on the roads, manned by Revolutionary Guards, he said.

“But we as Swiss we usually passed without problems. The problem was to prove that you were not a US citizen because they were looking for the Americans,” Koch said.

Many Iranians and expatriates were trying to flee Iran, Koch said. Asked if he recalled anything particular on the day of the now historic escape, he said:

“No, for us it was a regular flight as we operated every morning non-stop from Tehran to Zurich. The flights were always overbooked, we were one of the very few airlines still operating to Iran,” he said.

“There was always a big hassle at the check-in for last-minute tickets. Of course there were also problems for Iranians and foreign passengers because they were never sure they could leave the country or not. There were several immigration officers checking your documents, of course the Revolutionary Guards were also present.”

Koch, who said that he had seen “Argo” with his wife and son in Switzerland, said the Tehran airport security scenes rang true, including Revolutionary Guards questioning passengers.

“That’s realistic. When you went to the airport, you had these checkpoints before entering the building, you had checkpoints at the airport, then you had the official immigration, you had the Revolutionary Guards, and even before boarding the aircraft, the passports were checked again.

“And many passengers were stopped from leaving the country.”