Members of a campaign group called "Topple the Tyrants" took over the London mansion belonging to Libyan leader Moamer Gaddafi's son Seif al-Islam, saying it belonged to the Libyan people.
The mansion is a plush eight-bedroom neo-Georgian house in the exclusive Hampstead Garden Suburb district of north London.
They were soon joined by a handful of activists from the British Libyan Solidarity Campaign (BLSC) and celebrated by chanting "42 years -- enough is enough" from the roof, a reference to Gaddafii's time in power.
"Today we have occupied the £10 million ($16 million) mansion of Seif al-Islam in solidarity... with the people who are fighting and dying in Libya," a spokesman for "Topple the Tyrants" told reporters outside the mansion.
"We don't trust the British government to properly seize the Kadhafi regime's stolen assets.
"So we decided to take the matter into our own hands.
"Our aim is to make sure that the assets stolen from the Libyan people are returned to the Libyan people and not hidden away in some foreign bank account."
The demonstrators unfurled banners reading "Out of Libya, Out of London" and "Solidarity". They also waved the Kingdom of Libya flag used before Gaddafi's takeover in 1969.
The police have not thrown them out of the mansion.
The house, in a secluded, leafy close surrounded by some of Britain's most expensive residential streets, boasts an indoor swimming pool, a Jacuzzi, sauna and steam rooms and a basement cinema room with a four-metre wide screen.
It has a lacquered black and white kitchen, Venetian-polished plaster work, a coded key pad to the front door, underfloor heating and a control system operating the lighting, fireplace, curtains and blinds.
Seif, who studied at the London School of Economics, bought the house in 2009.
It was put up for sale again at a price of £10.95 million ($17.75 million) as the Libyan crisis unfolded, though it has since been taken off the market.
Managed through a holding company registered in the British Virgin Islands, it has also been available to rent at £9,750 a week.
Activist Belkasen Alghiryani, speaking in front of the Kingdom of Libya flag unfurled outside the front door, said: "If he sells this house, he is going to give the money to people so that they can kill Libyan people. We're not going to let it happen.
"We are not here to damage it. We are peaceful. We just want to make sure this house belongs to Libyan people and not to Seif.
"He stole our money; he killed our people."
A Scotland Yard spokesman told AFP police were called to the house after reports of unknown people entering the premises.
"This is being treated as a civil matter. There have been no arrests," he said.
"Police are monitoring the situation and safer neighbourhood reassurance patrols are taking place in the area."
