The group occupied Saif al-Islam’s eight-bedroom Georgian-style mansion and hung banners with anti-Gaddafi slogans from the roof.
They said they would stay until the £11 million ($16 million) house can be returned to the Libyan people.
“We do not trust the British government to properly seize the Libyan government’s corrupt and stolen assets so we have decided to take matters into our own hands,” said one of the occupiers.
Saif al-Islam had put the house on the market for over sixteen million dollars. However the mansion was withdrawn from sale last month.
A UK police spokesman said police have made no arrests and are treating the case as a civilian matter.
Britain has so far seized over three billion dollars of Gaddafi’s assets as part of sanctions imposed by the UN.
The activists who took Gaddafi’s mansion, however, blamed London for “actively helping to train the Libyan regime in crowd control techniques” and “training the regime in repression.”