Britain and the United States have been "very malign" influences on Iran over the course of decades, former foreign secretary Jack Straw has said.
Mr Straw's comments came as he returned from a visit to Tehran as part of a four-strong UK parliamentary delegation, which he said was "very well received" in the Iranian capital.
He said the parliamentarians detected a "lighter" atmosphere under the administration of President Hassan Rouhani, who took office last year on a reformist platform and is seeking better relations with the international community after years of isolation under Mahmoud Ahmadinejad.
But Mr Straw said that it was understandable that ordinary Iranians remain distrustful of the Western powers, due to UK and US involvement in the 1953 coup which unseated President Mohammad Mossadegh, support for Shah Mohammad Reza Pahlavi ahead of the 1979 Islamic Revolution and backing for Saddam Hussein during the Iraq-Iran War of 1980-88.
"There's a very very long history to this, to poor relations between Iran on the one hand and the United States and United Kingdom on the other," Mr Straw told BBC Radio 4's Today programme.
"If you were an ordinary Iranian you could be forgiven for thinking that over the decades the US and the UK have been a very malign force - and indeed we have been.
"We organised together a coup d'etat to remove a democratically elected president in my lifetime in Iran. We played a very, very bad and undermining hand as popular support for the Shah flowed away in the late 1970s. And then, for example, the West supported Saddam Hussein in a war which he provoked and for which Iran was the victim."
Mr Straw said he believed Mr Rouhani wants Iran to "come in from the cold", but warned that he faces opposition from conservative elements and could find his position "significantly" undermined if the West responds in the wrong way.
"There are any number of people amongst the conservatives who want to say that no good will ever come of visits from the West, and essentially want to isolate Iran from the West, whereas President Rouhani and his colleagues want a proper and normal relationship not only with the West but the rest of the world, and they want Iran to come in from the cold," said Mr Straw.
"What's important is that President Rouhani is there, he's very committed to change but he faces his own difficulties and how the West reacts to this can either help or significantly undermine him and so it's really important that we build up better understanding of the position of Iran.
"This never has been a one-man dictatorship. It's not a classic Western democracy by any means but there's a very lively political situation which President Rouhani has to navigate."
Mr Straw, who as Labour foreign secretary led efforts to secure a deal with Tehran over its nuclear ambitions, travelled to Iran with Tory MP Ben Wallace, former chancellor Lord Lamont and Labour left-winger Jeremy Corbyn, who are all members of the House of Commons All-Party Parliamentary Group on Iran and were invited by the British/Iran Friendship Group of the Iranian parliament.
He said that the delegation was "very well received, very well treated, had very good access" and had detected "considerable optimism" in the Iranian capital.
He said: "The thing that struck all of us was how much lighter the atmosphere was and certainly even lighter than when I was visiting Iran 10-12 years ago when President (Mohammad) Khatami, the reformist was in power but you could feel him being undermined both internally and externally."
Asked if the delegation spoke to dissidents during their visit, Mr Straw said: "We didn't want to, to be honest. It wasn't on the agenda. We were not in the business of making gestures. We were in the business of seeking to establish trust and good relations with people who want trust and good relations with us."