Around 250 sets of military night vision equipment sent to Tehran from Britain appear to have been passed on to the Lebanon-based militia group which it funds and supports.

They were sold under an export licence in 2003 to help the Iranians to monitor the desert and mountainous border regions with Afghanistan.

Despite the British Government’s current confrontation with Iran over its suspected nuclear weapons programme, the longstanding co-operative arrangement between Tehran and London over countering the heroin trade has produced effective results.

It is a relationship born of necessity. About 60 per cent of the heroin that reaches Britain and other European capitals comes from the poppy fields of Afghanistan, via Iran.

The battle to stem the flow of heroin and opium has resulted in the deaths of more than 3,500 Iranian anti-narcotics police since 1997.

Iran has publicly complained that its efforts to counter the drugs traffickers has been ignored by the West. However, Britain has pledged its full support to Tehran in this one area of co-operation. Customs and Excise officers, through drug liaison officers based in Islamabad, in Pakistan and in Tehran, have developed close links to their Iranian counterparts.

About 95 per cent of heroin which finds its way into Britain comes from Afghanistan, and then passes through the so-called Golden Crescent route through Pakistan and Iran. Up to 85 per cent of all heroin seizures takes place in Iran, indicating the scale of the Iranian counter-narcotics programme.

It was in recognition of the role Tehran could play that persuaded Britain to allow the sale of military night-vision equipment to Iran in 2003.

With much of the heroin trafficking taking place in remote border regions at night, it was judged to be crucial for the Iranian police to be able to operate effectively in the dark.

A report on the smuggling routes released by Customs and Excise in 2002 pinpointed how the smugglers ferried the drugs, mostly as unrefined opium at that stage, to mobile laboratories, operating in Turkey, Iran’s western neighbour.

Turkish drugs barons are the prime suppliers of heroin to the streets of Britain. Earlier this year a Turkish crime syndicate operating in Britain was convicted and imprisoned on drugs trafficking offences.

The support offered to Iran by Britain was taken a step further seven years ago when Robin Cook, then Foreign Secretary, agreed to increase collaboration with Tehran to try to stem the flow of heroin.

Mr Cook was responding to criticisms from senior Iranian politicians. Abdolvahed Mousavi-Lari, Iran’s former Interior Minister, had accused the Europeans of not doing enough to help Iran in the fight against the drugs traffickers.

He told a meeting at the UN: “The Europeans have not given us any serious help in the struggle against drugs to date. Iran is acting alone. Other states normally feel it suffices to send us conciliatory messages.”

Although this was not strictly true in Britain’s case — MI6 and other organisations had been engaged in covert anti-heroin operations — the Foreign and Commonwealth Office decided that it was time to offer more help.

Through the UN’s Drug Control Programme (UNDCP), Britain supplied Tehran with bullet-proof vests, and soon afterwards, Mr Cook visited Tehran where he was told of other equipment shortages, including night-vision equipment.

Underlining the British efforts, Mr Cook made a statement praising the work of MI6 intelligence officers in tackling the drugs traffickers. It was partly in recognition of the secret collaborative work carried out with the Iranians.

In one six-month period in 2000, Iran seized 163 tonnes of opium and heroin, most of it heading for Europe. One shipment, carried on camels, weighed two tonnes.

The UNDCP opened an office in Iran in January 2000, and allocated about £6 million to Tehran’s campaign against the traffickers. The UN said in a statement: “Iran fights a war alone”. However, even the US, with its strong anti-Iranian position, agreed to take Iran off its list of countries supporting drugs trafficking.

Times Recommends

• Green activists 'are keeping Africa poor'
• 'Delayed justice' fear for OJ Simpson
• Sex and the sari