The Mujahideen are a 4000-strong anti-Iranian dissident army, currently under US protection in a camp in Iraq. They have a vociferous public relations campaign in Britain and the backing of some Washington neo-conservatives.

The group, known as the "tank girls" because of the preponderance of women in its ranks, has also won the support of the Daily Telegraph, which wants it to help overthrow the mullahs in Tehran. It says in a leader: "We should back the main resistance group, the People's Mujahideen ... Give them the tools and they will finish the job".

There is a growing right-wing campaign in parts of Washington and London for regime change, citing Iran's nuclear ambitions. But leftwing UK figures have also joined the campaign to legitimise the Mujahideen, whom they see as freedom fighters.

An advertisement by supporters in the Guardian last month quoted Labour peer Lord (Robin) Corbett, as well as Liberal Lord (David) Alton and Tory backbencher David Amess in support, along with human rights lawyers Imran Khan and Geoffrey Bindman.

However, the foreign secretary, Jack Straw, calls them a "a nasty terrorist organisation" and British officials are barred from contact. The Mujahideen are officially proscribed but their British backers want the terrorist designation lifted.

Refugees from the Mujahideen we traced in the Netherlands include Ardeshir Pahrizkari, who walks on crutches. His back and feet were broken, he told us, when he was punched, kicked and had chairs thrown at him at a mass meeting to denounce him organised by his commander.

His crime, he says, was to object to "self-criticism" sessions and the beating up of internal dissidents. "They use Stalinist methods to get rid of even a spark of opposition".

At the time, the "tank girls" were being financed by Saddam Hussein in camps in Iraq. The army was allocated illicit cash from the UN oil-for-food programme, according to Iraqi ministry documents.

Mr Pahrizkari says he was handed over to Saddam's secret service, who took him to Abu Ghraib prison. There were continual beatings there, he said. "When the Red Cross came round, we were told: 'Any contact with them and we will break every bone in your hands and feet.'"

His fellow refugee, Akbat Akbari, says he was tortured extensively, and is still having psychological counselling, after three years in Abu Ghraib.

"The moment you arrived, you were beaten on the soles of the feet. Prisoners were used to hoist your feet in the air with ropes."

Later, he says, his toenails were pulled out. Pepper and salt were forced into his anus.

He says he was falsely accused by the Mujahideen army of being an Iranian spy. Eventually both men were handed over to their enemies in Iran.

They claim they escaped, and deny they are working for the Iranian regime. "My father, brother and sister were imprisoned for six months after I escaped," says Mr Akbari. "The regime took their house."

Mr Pahrizkari says: "I want to warn people not to fall into this trap. If the Mujahideen are the next potential regime in Iran, then that regime will be a dictatorship".

The two men's testimony is supported by last week's New York-based Human Rights Watch report. It says telephone interviews with 12 other former Mujahideen soldiers "paint a grim picture of how the organisation treated its members". Witnesses alleged two cases of deaths under interrogation.

A former English soldier in the MKO, Anne Singleton, now living in Leeds, talked to the Guardian last week. She said the MKO was a brainwashing cult, which ordered its members alternately to divorce and re-marry. As a "Tank girl", she says she wielded a Kalashnikov in the Iraqi deserts with a battalion of women equipped with tanks and revolutionary slogans. They are run by Maryam and Massoud Rajavi, who are married.

She believed she was joining a feminist marxist battle group dedicated to the overthrow of Iran's misogynist clerics. But she says she was deceived and is horrified UK politicians are backing dangerous fanatics.

Young supporters burned themselves to death in 2003, one in London, in coordinated protests after the arrest of some leaders, and the Mujahideen army is accused of numerous bombings inside Iran.

The group raised up to £5m a year in Britain through a charity called Iran Aid, until the Charity Commission closed it down in 2001, saying it was unclear where the money was going.

Lord Corbett's response to the Human Rights Watch report is: "All the people they interviewed are agents of Iranian intelligence. A bill is going through the US Senate allowing financial aid to opposition groups in Iran. People are desperate to stop the Mujahideen getting any of the money".

He attacks the methodology of the report and accused Ms Singleton of also "having links with the Iranian ministry of intelligence".

Ms Singleton denies this, saying: "To claim that every western government and humanitarian organisation which criticises the Rajavi cult is somehow connected to the Iranian secret services shows Lord Corbett's own refusal to take responsibility for supporting this terrorist cult."