A respected Iranian political analyst employed by the British embassy in Tehran is facing a lengthy prison sentence after he was charged yesterday with “acting against national security”.

The charge was a sharp escalation of the hardline Iranian regime’s campaign to blame Britain for instigating demonstrations against last month’s disputed re-election of President Mahmoud Ahmadinejad.

Hossein Rassam, the senior Iranian employee at the embassy and a close confidant of the ambassador, Simon Gass, was arrested last Saturday at his home. Eight other Iranian employees of the embassy were also detained.

Seven have been released and another locally employed member of staff from the political section is expected to be freed soon. However, Rassam, 44, has been incarcerated at the notorious Evin prison.

Employed at the embassy since 2004, Rassam is a leading political analyst, whose opinions have been sought by foreign diplomats and journalists.

Sources in Tehran ridiculed the charges as trumped up by a regime desperate to find a propaganda “pawn” in their efforts to hold foreign powers responsible for the protests.

Western diplomatic sources cast serious doubt on an allegation by Ayatollah Ahmad Jannati, head of the powerful Guardian Council responsible for monitoring the elections, that Rassam had “confessed”.

Yesterday, sources in Tehran said they believed Rassam faced only a “show trial”. None of the seven embassy employees released have returned to work after their jailers told them to stop working for the British.

Abdolsamad Khorramshahi, Rassam’s lawyer, said: “We have prepared and submitted the defence documents and I have to see the judge \ week.” Khorramshahi, a well-known human rights lawyer in Tehran, said he had not been able to meet his client and nor had anyone from the British embassy.

The British are bearing the brunt of the regime’s rage against foreign “interference”. Ayatollah Ali Khamenei, the supreme leader, who is a supporter of Ahmadinejad, denounced Britain as the “most evil” of Iran’s challengers.

The regime may be about to clamp down on Mir Hossein Mousavi, Ahmadinejad’s opponent, who has refused to concede defeat and lambasted the government as “illegitimate”. He has been under virtual house arrest since the election.

A senior adviser to Khamenei yesterday called Mousavi an American stooge. “It has to be asked whether the actions of \ are in response to instructions by American authorities,” said an editorial in Kayhan, the conservative mouthpiece.

It was written by Hossein Shariatmadari, Kayhan’s editor, infamous in Iran for helping to frame questions for agents interrogating prisoners in Evin prison, and considered a spokesman for the regime.

Shariatmadari said Mousavi and his supporter Mohammad Khatami, the former reformist president, should be tried for “horrible crimes and treason”. It is a serious charge: treason carries the death penalty in Iran.

Sources in Tehran, deeply concerned by the imprisonment of Rassam, pointed out that both he and his wife Maryam had been fully vetted by the Iranian foreign ministry and intelligence services.

“He is an Iranian patriot,” said Frances Harrison, a former BBC bureau chief in Tehran. “He could have left Iran but his loyalties were with his country.”

The charges against him were vehemently denied by David Miliband, the foreign secretary. “We are urgently seeking clarification from the Iranian authorities,” Miliband said. Last night he was scheduled to speak to Manouchehr Mottaki, the Iranian foreign minister.

London is likely to seek stronger international pressure against Iran if the trial of Rassam proceeds.

British diplomats are liaising with their European Union counterparts to present Iran with a united front, including tighter sanctions. The EU is Iran’s largest trading partner.

Last week, the EU agreed to summon the Iranian ambassador in each country and make clear there would be no “business as usual” until the embassy employees were released.

Tougher measures will be discussed this week at the G8 summit in Italy. None of the member nations wants to cut ties with Iran, because they need to engage in talks on the country’s nuclear programme.

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