By Justin Parkinson
BBC News political reporter, Parliament Square
They were tired. They were irritated. They were staying put.
Hundreds of Tamil protesters camped out in Parliament Square, having been moved on from nearby Westminster Bridge, which they had blocked overnight with a mass sit-down demonstration.
The square, usually occupied only by full-time anti-Iraq war campaigner Brian Haw and a few colleagues, was bustling with people.
A day after their demonstration - aimed at getting Gordon Brown to push for an end to the civil war in Sri Lanka - began, the anger was still evident.
Occasionally part of the crowd surged towards the dozens of police ringing the square, which is effectively a large traffic island with two lanes of heavy traffic circling it, overlooked by a statue of Sir Winston Churchill.
The scuffles moved aimlessly from one side of the green to the other, and then back again.
A few missiles were thrown at police, accompanied by some unprintable words about the UK government.
Four people were arrested: one for violent disorder, another for breach of the peace and two for public order offences.
Some protesters needed medical treatment, including one young man with blood spattered down his shirt and another who suffered minor head injuries.
I've been in England for 10 years now and I've always respected the police. But now I have lost all of that respect.
But most of the time the demonstrators - mainly in their twenties and thirties - just stood around or sat down, talking to each other or chanting slogans like "ceasefire now" and "end the genocide", as a few of their number banged drums.
They waved banners making the same points.
The police, who were filming the protest, have come in for criticism. Some protesters said officers had been heavy-handed in moving them on from Westminster Bridge.
One told the BBC: "I've been in England for 10 years now and I've always respected the police. But now I have lost all of that respect.
"The police are terrible in the way they have handled themselves. They are despicable."
A helicopter hovered above Parliament, while two RNLI boats were stationed a few metres from the bridge, ready in case any more Tamils jumped into the Thames, as a two had done overnight.
The BBC's Colette McBeth at the scene of the protests
They were determined to get UK media coverage for the Sri Lankan situation. They succeeded.
In recent weeks the clashes between Sri Lanka's army and Tamil Tigers - who are fighting for a separate state - have intensified.
Security forces say they are making a final push to defeat the rebels and end nearly 30 years of conflict.
The United Nations estimates more than 2,800 civilians have been killed and 7,000 others injured in the fighting in the north-east of Sri Lanka in the last two months. The country's government disputes these figures.
Some of the protesters on Parliament Square said they would not move until the UK government increases pressure on the Sri Lankan government to end the war.
One of them said: "This has been a peaceful protest. We are well behaved but we are angry. Someone has got to let the British government know what is going on.
"Thousands of people are dying. Something must be done."
Across the road, by the Palace of Westminster, tourists took photos and filmed the demonstrations.
Most seemed as clueless about what was going on as the commuters who arrived late for work on Tuesday morning as Westminster Tube station was closed by police.
A sleepless night behind them, the Tamil protesters seemed to harbour no intention of heading off for a rest.
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