For decades Iran’s ayatollahs have insisted that, despite all the evidence to the contrary, their nuclear intentions are entirely peaceful, and forcefully rejected any suggestion that they seek to acquire nuclear weapons.

Even when presented with highly incriminating proof provided by Western intelligence agencies like the CIA that Iran seeks to build nuclear weapons, the regime has pointed to a fatwa allegedly issued by the country’s Supreme Leader, Ayatollah Ali Khamenei, that prohibits Iran from acquiring nuclear weapons.

The fatwa is said to originate from comments Mr Khamenei made in 2003 forbidding the production and use of weapons of mass destruction, which the regime has conveniently referred to when questioned about undeclared aspects of its nuclear programme, such as the Natanz uranium enrichment facility which has the ability to produce material for nuclear warheads.

Moreover, Western leaders have naively taken Iran’s denials of bad behaviour at face value. Former US President Barack Obama, for example, as part of his ill-judged effort to agree a nuclear deal with Tehran, the Joint Comprehensive Plan of Action (JCPOA), declared in his address to the UN General Assembly in 2013 that: “The Supreme Leader has issued a fatwa against the development of nuclear weapons.”

Now Iran’s protestations of innocence lie in tatters following the extraordinary admission by one of the country’s leading nuclear experts that Iran has maintained a clandestine nuclear weapons programme for many years. In an interview published on the eve of the reopening of talks in Vienna aimed at reviving the JCPOA,, Fereydoun Abbasi-Davani, who formerly headed the Iranian Atomic Energy Organisation, revealed that Iran had created a “system” to develop an atomic weapon in spite of the Supreme Leader’s fatwa.

The purpose of the interview, given to mark the first anniversary of chief Iranian nuclear scientist Mohsen Fakhrizadeh, was to explain the late scientist’s working methods. Instead, Mr Abbasi-Davani, wittingly or otherwise, provided the first confirmation by a senior regime official of Iran’s long-held ambitions to acquire nuclear weapons: “Although our stance on nuclear weapons based on the Supreme Leader’s explicit fatwa regarding nuclear weapons being forbidden is quite clear, Fakhrizadeh created this system, and his concern wasn’t just the defence of our own country,” Mr Abbasi-Davani explained. In other words, Iran’s intention all along has been to develop weapons that can be used to threaten its adversaries in the region such as Israel.

In many respects, Mr Abbasi-Davani has done the world a great favour, as his helpful explanation means that, with the resumption of nuclear talks in Vienna aimed at reviving the JCPOA, Western negotiators no longer have to labour under the fiction that Iran’s nuclear intentions pose no threat.

And while Mr Abbasi-Davani’s revelations present an inconvenient truth for Iranian apologists like Lord Lamont of Lerwick, the chairman of the British-Iranian Chamber of Commerce, they should encourage the West to take a far harder line with Iran, whose participation in the Vienna talks is aimed more at getting economic sanctions lifted than making any real concessions on its nuclear activities.

Iran’s attitude towards the talks, which reconvened in Vienna at the start of this week, was summed up in the draft document it submitted, which placed the emphasis on Western leaders agreeing to lift sanctions, with only minimal concessions offered on its nuclear activities.

This prompted America’s usually dovish Secretary of State Antony Blinken to play down any possibility of a breakthrough. “I have to tell you, recent moves, recent rhetoric, don’t give us a lot of cause for optimism,” he said.

Iran’s approach prompted Israeli Prime Minister Naftali Bennett to call for the “immediate cessation” of the talks.

Indeed, if anything, Iran’s attitude has become far more confrontational since the election of hardline cleric Ebrahim Raisi in the summer. Britain has accused Iran of subjecting international nuclear inspectors to invasive physical searches in an intimidation campaign designed to block monitoring of sensitive nuclear facilities.

And while the Biden administration still clings to the belief that the nuclear deal can be revived, US military officials are less convinced. At the recent Manama Dialogue security conference in Bahrain, senior US military officers made it clear that military solutions for dealing with Iran’s nuclear programme were very much on the table.

Israeli Foreign Minister Yair Lapid, who met with Foreign Secretary Liz Truss in London last week, takes a similar view, warning that only a credible military threat will stop Tehran’s nuclear programme.

Certainly, given the appalling prospect of Iran acquiring nuclear weapons, the world can no longer accept Iran’s bare-faced lie that its nuclear intentions are peaceful.