Students are planning a mass demonstration outside the British Embassy in Tehran today, warning that it could trigger a repeat of 1979, when students stormed the US Embassy and held 52 diplomats hostage for 444 days.

The Foreign and Commonwealth Office ordered the evacuation of the families of the 22 British diplomats and warned British citizens against any non-essential travel to Iran.

As the regime stepped up its efforts to blame the “little Satan” for the turmoil engulfing the Islamic Republic, Iranian MPs urged the foreign ministry to curtail ties with Britain. There was speculation that the British Ambassador would soon be expelled.

The growing tensions will not help British government efforts to secure the release of the three remaining hostages held by an Iranian-backed Shia group in Iraq.

Ayatollah Ali Khamenei, Iran’s Supreme Leader, launched the rhetorical war against Britain last Friday by labelling it the “most treacherous” of various Western powers that were using the presidential election to destablise the Islamic Republic. On Sunday the regime expelled the BBC correspondent Jon Leyne and claimed that agents of the British secret services had been infiltrating Iran “in droves”.

Today’s government-orchestrated demonstration outside the embassy will target the “perverted Government of Britain for its intervention in Iran’s internal affairs, its role in the unrest in Tehran and its support of the riots”.

Esmail Tahmouressi, a student leader, warned that the demonstration could be another “November 4” — a reference to the storming of the US embassy in the heady days after the revolution. He said the embassy should be closed because “there cannot be a compromise with the old fox, Britain”. The diplomats are expected to turn up to work but the Foreign Office refused to comment, beyond saying it was monitoring the situation closely.

The embassy, the ambassador’s residence and its extensive grounds are ringed by 10ft-high walls. It employs about 100 Iranian citizens and has Iranian guards. It is the target of regular protests. Demonstrators have managed to get inside before — most recently in late December when they took to the streets over the Israeli invasion of Gaza.

The diplomats mostly live in another compound in northern Tehran, and their families are expected to fly out soon. Speculation that they could soon be joined by Simon Gass, the ambassador, was fuelled by Hassan Ghashghavi, a spokesman for the foreign ministry, when he said: “I cannot confirm this. Neither can I deny this.”

A spokesman for the Iranian parliament’s foreign relations commission said it had asked the Foreign Minister to curtail Iran’s relations with Britain.

Elsewhere in Tehran about 1,000 demonstrators tried to mount a vigil, but were dispersed by several hundred police and Basiji — volunteer militiamen — using teargas. Sixty demonstrators were arrested, adding to the 457 detained over the weekend.

Amid reports of unhappiness within the police, the elite 150,000-strong Revolutionary Guard — which has yet to be deployed — issued a statement threatening a “decisive and revolutionary” response to further demonstrations.

Ayatollah Khamenei installed one of his own men, Mohammad Ali Jafari, as the force’s commander in late 2007, and has purged an older generation reluctant to move against its own people. “It looks like they were planning this all along,” one Iranian analyst said.

Even more ominously, the head of the parliament’s judiciary committee raised the possibility of Mir Hossein Mousavi, the man defeated by Mahjmoud Ahmadinejad in the disputed presidential election, being arrested. Mr Mousavi’s call for “illegal protests” were criminal acts and should be confronted, Ali Sharokhi said. “The ground is paved to pursue Mousavi legally.”

Tomorrow the Guardian Council, a body of senior clerics, is expected to announce the result of its investigation into charges that the presidential election was rigged, but nobody believes that it will overturn the result.

Abbasali Kadkhodai, a spokesman, admitted yesterday that in 50 districts the votes cast in the election exceeded the number of eligible voters.

He made clear, however, that Mr Ahmadinejad’s victory would not be affected even if the results in the 50 districts were reversed. They accounted for only 3 million votes, and the official results show that Mr Ahmadinejad won by a margin of 11 million.

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