It has emerged that a foreign government delivered the warning to Britain in early 2004.

Separately, it has been disclosed that the system was sold to Iran by a former senior member of the Ukrainian security service. The deal was brokered by an organised crime boss and, it is feared, contributed to the Iranian nuclear programme that is now the subject of an international confrontation.

Iran had also been using large cash payments to lure technical and scientific staff from Ukraine to work on its nuclear programme. Other targets of the bribes included one former head of Ukrainian intelligence, who was offered $5m (£2.6m) to help the rogue state, but he rejected it.

It has also emerged that in 2004 the Ukrainian government was investigating the transport of weapons from Iraq to Syria and Iran before the war to topple Saddam Hussein. Now that the row over Saddam’s weapons has died down, however, it is Iran’s nuclear programme that is the more controversial issue.

Britain’s policy of trying to use quiet diplomacy to curb the Iranian plans has been in stark contrast to the more bellicose rhetoric coming from America.

British ministers have never disclosed, however, that they were given warnings as long ago as 2004 that Iran had gone to the extent of covertly acquiring missiles capable of carrying nuclear warheads.

The latest escalation of the nuclear crisis came last week, when Iran missed a United Nations deadline to stop enrichment of uranium, after which President George Bush said, “There must be consequences”, adding that the world faced “a grave threat from the radical regime in Iran”.

Mahmoud Ahmadinejad, the Iranian president, responded by calling the claim that his country aimed to develop nuclear weapons “a sheer lie”. Iran insists its nuclear programme is for electricity generation.

Britain is playing a central role in the standoff between the UN and Iran over its nuclear programme, both as a permanent member of the security council and as one of the three European Union negotiators.

The prospect of Iran developing nuclear weapons has alarmed the international community partly because of extreme statements by Ahmadinejad — such as his call for the destruction of the state of Israel — and partly because of the country’s funding of terrorist groups such as Hezbollah fighters in Lebanon. Iranian-made bombs and weapons have also been used against British troops in Iraq.

The International Atomic Energy Authority has been repeatedly thwarted in its attempts to establish the scope and purpose of the Iranian nuclear programme. An authority source said the extent of its investigations into Iranian attempts to acquire hardware for nuclear weapons was a “moot point”. He did confirm the agency was aware that Ukraine had been a “key player in the process”.

Last year, Ukrainian prosecutors announced they were investigating the illegal sale of at least 18 cruise missiles to Iran and China in 2001.

The Ukrainians were supposed to have destroyed or transferred to Russia their share of the former Soviet nuclear arsenal. The Americans funded a massive disarmament project, but considerable amounts of weaponry are thought to have disappeared in the interim period.

Ukraine also inherited hundreds of thousands of tons of conventional weapons from the Soviet Union, some of which have been decommissioned and some sold abroad, either legally or illegally.

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