Twelve held at Parliament protest
At least 12 people were arrested after police and protesters clashed outside the Houses of Parliament.
The plan had been to stage what was described by protesters as a peaceful Halloween picnic in Parliament Square.
From midnight, about 150 people began showing their opposition to a bill to be debated later, which would make squatting a criminal offence.
Violence flared as police tried to move them on. It is an offence to stage unauthorised protests at Westminster.
About 50 people, who had refused to leave, were held within a cordon as police picked out individuals and arrested them, said the BBC's Keith Doyle at the scene.
He said: "Police used batons as more arrests were made and eventually at around 03:00 the remaining protesters were allowed to leave, although they say they plan further shows of opposition to the bill."
Police had been concerned the protesters would try to set up a camp similar to the one at St Paul's Cathedral.
The Legal Aid, Sentencing and Punishment of Offenders Bill is to be debated in the Commons later.