They came looking for trouble. . they got their wish

The smiling faces of clowns greeted curious onlookers and the huge media pack at what had been billed as the start of the Carnival of Full Enjoyment.

At midday, the ragtag army gathering in Shandwick Place did seem to the casual observer intent on nothing more than enjoying themselves.

Whistles blew and drums beat to a samba rhythm.

The only ominous sign of things to come was the presence of a handful of anarchists dressed in black, members of the notorious Ya Basta movement, who tried to disrupt Saturday's Make Poverty History march.

But the antics of hundreds of fancy-dressed revellers on Edinburgh's streets were overshadowed in one sudden moment.

At precisely 1pm, and with no warning, the all-in-black figures, who had gradually grown in number, decided to storm the line of police preventing the protesters from continuing their noisy march.

They didn't get very far, but the atmosphere of the day changed and the carnival spirit never really came back.

An air of menace, rarely felt in the centre of the Capital, hung in the air for the rest of the day and into the night.

Within the melee that unfolded among the mob of hundreds of protesters corralled by police on Canning Street, near the Capital's financial district, the scene was often chaotic.

One anarchist fell and vomited on the street, another collapsed and said he couldn't breathe. A woman said she was kicked by an officer, people called for medics and the anarchists' legal team screamed about human rights.

But the police weren't letting anyone out, not even some terrified female journalists, and the majority of protesters were to spend the next four hours stuck inside the police trap.

One anarchist from Sussex, carrying a sign with a baby doll's head impaled on top of it, stood at the front of the crowd and shouted at the officers. The 21-year-old said: "We're not violent or dangerous, we're just against oppression. We're here to enjoy ourselves."

An angry-looking woman stormed past, wearing a T-shirt with a picture of Ronald McDonald and the word "Satan".

One protester managed to scale a wall overlooking the street, around 25ft up. Waving a black flag, he threatened to urinate over officers, before he turned around and seemingly contemplated defecating instead. Fortunately, he changed his mind and was content to bare his buttocks to the cheering crowd.

There was a surreal quality to events at times as legal advice was dished out to the demonstrators by protest organisers.

Legal experts from the radical Dissent network wandered around the group, handing out advice on what to do if arrested. Others played football with a stolen police officer's hat, aware they were in for a long haul.

It wasn't quite the same on Princes Street, where the Infernal Noise Brigade - a band of 20 musicians dressed in orange and black - had missed the start of the now infamous Carnival for Full Enjoyment, and were staging their own march.

They started off by harmlessly pulling faces at the lines of police stretched across Princes Street, but as numbers swelled, the anarchists began a direct challenge against both riot police and mounted officers.

Protesters blowing whistles stood on top of bus stops, while others flying flags and dressed in black cheered and clapped. The tension was briefly broken when a naked protester ran along Princes Street with two clowns in tow to the delight of bystanders.

But the sinister presence of the anarchists, their faces covered with scarves, was clearly unnerving for all involved.

Princes Street was overrun with more than 40 police vans, and crowds of people, including hundreds of members of the public, were herded on to The Mound as officers tried to control the demonstration. As riot police tried to push half of the protesters into a section of Princes Street, shoppers and tourists were told to stay away and forcibly pushed back.

Some people could be seen inside the police cordon receiving treatment for head injuries, while around them the demonstrations continued. When the group, now numbering around 250, was forced into Princes Street Gardens at about 2.30pm, there was a look of glee on their faces - and fear on those of innocent passers-by.

Flowers were uprooted and benches commemorating loved ones were torn from the ground and hurled at officers. But then, as in Canning Street, the protesters realised they were stuck. So members of the Clandestine Rebel Insurgents Clown Army began replanting the flowers and other anti-capitalists sat on the grass to enjoy a picnic.

One clown said: "We are really here to keep people happy, keeping the crowd happy and keeping the cops happy."

On Waverley Bridge, where another group of protesters was being held, somebody used a feather duster on a policeman's riot gear, while another used bright pink lipstick to draw a smiling face on a shield.

On Princes Street, where yet another crowd was being detained, anti-capitalists spent their time banging drums and throwing a beach ball around.

One protester wearing a monkey mask climbed on to a traffic light to view the spectacle.

Some said the police reaction had been over the top, while others, including visitors, were upset by the actions of the protesters.

When police tried to reverse their vans along Princes Street, they found themselves surrounded by protesters, who stopped the vans from moving while they hurled bottles and sticks. Back in Canning Street

there were more skirmishes when police decided to send the protesters home, and a number of people were dragged kicking and screaming by officers.

Meanwhile, at an evening skirmish outside Sainsbury's on Rose Street, there was real panic as the public - many of whom were just being curious - ran in droves from the oncoming lines of mounted police. Suddenly the bang of drums was replaced by the noise of smashing glass while bricks and pallets were hurled at the unflinching officers.

However, as quickly as the tension built, it dissipated once more, with only a handful of protesters left on Princes Street playing football within the police cordon. By 8.30pm only several hundred protesters remained in Princes Street. The football was confiscated by police, sparking threats of a riot, but there didn't seem enough energy left among the demonstrators.

When the police cordon was broken, most headed up to Bristo Square, where the Dissent network has converged in the Teviot House student union.

A small, hard-core group of skinheads, mostly from Edinburgh and probably not anti-capitalists, caused some trouble outside a McDonald's late at night.

But the majority of protesters sat outside Teviot House drinking beer and smoking cannabis, dissecting the day's events.