Gaddafi's son Saif tried to sell the property after his family's multi-billion pound fortune was frozen around the world. The house has a swimming pool, sauna, Jacuzzi and suede-lined cinema room.
Speaking from the roof, the group's leader, using the pseudonym Montgomery Jones, said: "We want to make sure the property goes back into the hand of the Libyan people who deserve it. We're here for a serious reason, we're not here to luxuriate: I don't think what we are doing is legal but I don't think it's relevant if you are talking about something this important."