‘You are the sun of Islam, shining on the universe!” This is how Muhammad Khatami, the mullah who was president of Iran until last year, described Hezbollah last week. It would be no exaggeration to describe Hezbollah — the Lebanese Shi’ite militia — as Tehran’s regional trump card. Each time Tehran has played it, it has won. As war rages between Israel and Hezbollah in Lebanon, Tehran policymakers think that this time, too, they can win.

“I invite the faithful to wait for good news,” Iran’s President Mahmoud Ahmadinejad said last Tuesday. “We shall soon witness the elimination of the Zionist stain of shame.”

What are the links between Hezbollah and Iran? In 1982 Iran had almost no influence in Lebanon. The Lebanese Shi’ite bourgeoisie that had had close ties with Iran when it was ruled by the Shah was horrified by the advent of the clerics who created an Islamic republic.

Seeking a bridgehead in Lebanon, Iran asked its ambassador to Damascus, Ali Akbar Mohtashamipour, a radical mullah, to create one. Mohtashamipour decided to open a branch in Lebanon of the Iranian Hezbollah (the party of God).

After many meetings in Lebanon Mohtashamipour succeeded: in its founding statement it committed itself to the “creation of an Islamic republic in Lebanon”. To this end hundreds of Iranian mullahs, political “educators” and Islamic Revolutionary Guards were dispatched to Beirut.

Within two years several radical Shi’ite groups in Lebanon, including some with Marxist backgrounds, had united under the Hezbollah name and became the main force resisting the Israeli occupation of Lebanon after the expulsion of Yasser Arafat’s Palestine Liberation Organisation (PLO) in 1983.

Terror has been its principal weapon. Throughout the 1980s Hezbollah kidnapped more than 200 foreign nationals in Lebanon, most of them Americans or western Europeans (including Terry Waite, the Archbishop of Canterbury’s envoy). It organised the hijacking of civilian aircraft and more or less pioneered the idea of suicide bombings against American and French targets, killing almost 1,000 people, including 241 US marines in Beirut and 58 French paratroopers.

The campaign produced results. After Hezbollah’s attacks, France reduced its support for Saddam Hussein. America went further by supplying Iran with TOW anti-tank missiles, shipped via Israel, which helped to tip the Iran-Iraq war in favour of Iran. In exchange Iran ordered Hezbollah to release French and American hostages.

Once the Iran-Iraq war was over, Tehran found other uses for its Lebanese asset. It purged and then reshaped Hezbollah to influence the broader course of regional politics while using it to wage a low-intensity war against Israel.

In 2000, when the Israelis evacuated the strip they controlled in southern Lebanon, Tehran presented the event as the “first victory of Islam over the Zionist crusader camp” and Hezbollah was lauded across the Arab world. Hezbollah taunted the Israelis with billboards on the border reading, “If you return, we return”.

To prop up that myth, Tehran invested in a propaganda campaign that included television “documentaries”, feature films and books and magazine articles. The message was simple: while secular ideologies — from pan-Arabism to Arab socialism — had failed to liberate an inch of Arab territory, Islamism, in its Iranian Khomeinist version working through Hezbollah, had achieved “total victory” over Israel in Lebanon.

Since 1984 Iran has created branches of Hezbollah in more than 20 countries. None has equalled the success of the Lebanese branch, which until recently enjoyed something akin to cult status among Arabs, including non-Muslims, because of the way it stood up to Israel.

It has not even cost Iran very much. Hezbollah was launched with just £13m. After that, according to best estimates, Iran spent £32m to £54m a year on its Lebanese assets. Even if we add the cost of training Hezbollah fighters and equipping them with hardware, Hezbollah (the strongest fighting force in the Middle East after Iran and Israel) has not cost Iran more than £1.3 billion over two decades.