By Sue Lloyd-Roberts

The faceless men from the ministry called me on the mobile phone. "We are deporting you tomorrow morning because you have taken pictures of prostitutes. This is not a true reflection of life in our Islamic Republic. We don't have prostitutes."

But it was hard not to take pictures of prostitutes. Walking out of the Laleh Hotel, a favourite for journalists in Tehran, they are waiting under the trees in the nearby park and climbing into the cars which kerb crawl along the wide avenues.

Many girls run away from home because they can't bear the lack of freedom - they prefer to become prostitutes than face the restrictions

Leilah, 19

"I started selling sex at 11," 19-year-old Leilah says. She looks 30.

"There are 10 and 11-year-olds on the street as well. I had to do it because my stepmother turned me out of my home and my father dumped me here.

"But not all of us do it in order to survive. Many girls run away from home because they can't bear the lack of freedom. They prefer to become prostitutes than face the restrictions."

A reporter working for a woman's magazine said she believes there are more than one million women who sell their bodies in Tehran, which has a population of 10 million.

"I would say one in three women do it," she says.

"Some do it out of despair, runaway teenagers do it to survive and some middle-class girls do it just to put two fingers up at the regime - to take off their black chadors and taste freedom."

She asks to be kept anonymous. If a foreign journalist can be deported for telling unsavoury truths, a local reporter can be imprisoned.

Rebellious teenagers

In the wealthier suburbs in northern Iran, the girls have their headscarves pushed as far back off their faces as possible.

Sure, I've been flogged for taking drugs and I've been flogged for listening to [music]

Arash, 16

Nazenin reveals slashes of bright eye shadow to match her powder blue scarf.

How does she get away with make-up which would have earned her a flogging only a couple of years ago?

"I think the mullahs are giving us more leeway these days so that they can get up with their own business," she says.

"They want us to be distracted by make-up and drugs. They allow tonnes of drugs to enter the country and create millions of addicts."

Two 16-year-old boys give the girls knowing looks as they pass. They both have long hair and trainers. It is easier for the male to dress the part of the rebellious teenager than for a girl in Iran.

"We get drugs and alcohol whenever we can," says Arash. "Sure, I've been flogged for taking drugs and I've been flogged for listening to a personal walkman while walking down the street. We hate the lack of personal freedom in this country."

'No joy'

When Ayatollah Khomeini returned to Iran to lead the revolution 23 years ago, he was honest enough to warn the people of the new Islamic Republic that "Islam offers no joy".

We hate the way we have to behave and dress - the Koran does not say we have to cover up like this

Fatima, 23

It is the joylessness of life which young people complain about. Fatima stopped to talk to me as I walked past the "Death to Israel" rally in Tehran, an annual ritual where hundreds of people are bussed into the city to shout obscenities against Israeli Prime Minister Ariel Sharon and US President George W Bush.

She was embarrassed. "Most of us don't think like that, at least the educated ones who have read about how Iran was before the revolution," the pretty 23-year-old says later, surrounded by screaming women draped in shroud-like black chadors.

"We hate the way we have to behave and dress. The Koran does not say we have to cover up like this.

"The mullahs force us to wear veils not to support Islam but to control us and to further their own political interests. Young people in Iran are unhappy and women especially are desperate."

Morality police

Another girl in her 20s told me about the Thursday night parties - with music and alcohol - she holds at her home. But they do not always get away with it.

A few weeks ago, the morality police burst into the house dragged them all down to the police station and gave them each 80 lashes.

I asked the government spokesperson for women's affairs, Nazra Koolaee, three times whether she agreed with such a punishment. Each time she refused to answer.

She did, however concede that the stoning of women to death for adultery was an "inefficient" means of dealing with the problem.

Mrs Koolaee is regarded as one of President Khatami's reformers. Does she intend to do away with the practice? All she could say mournfully was "we hope, we hope".

The Ministry of Islamic Guidance, which monitors all journalistic activity in Iran, gave me permission to report on social change in Iran yet I was deported for taking pictures of prostitutes and talking to a student.

It could, alas, be a long time before Iran abandons the practice of flogging partying students and stoning women to death.

Sue Lloyd-Roberts' report will be on Newsnight tonight at 2230 on BBC2