"At this time this is being treated as a civil matter. There have been no arrests," a Scotland Yard spokesman told AFP. "Police are monitoring the situation and safer neighbourhood reassurance patrols are taking place in the area," they added.
The house has an indoor swimming pool, a sauna room and a cinema room. Saif bought the house in 2009.
"We do not trust the British government to return it to the people of Libya because they have a long history of helping the Kadafi regime," "Topple the Tyrants" spokesman Montgomery Jones told a British newspaper.
"Our aim is to make sure that the assets stolen by Kadhafi are returned to the Libyan people and don't disappear into the pockets of governments or corporations," he said.
Jones invited refugees from the conflict in Libya and others "fleeing oppression around the world" to come to the house.
Seif put up the house last month for 12.75 million euros as protests began in Libya, but it has now been taken off the market.
Mike Freer, a British MP representing the Finchley and Golders Green constituency, has called for the house to be seized and for Seif to be barred from entering the UK.
"Other members of the Gaddafi family have tried to escape the anger of the Libyan people by flying to Malta and the Lebanon but have they have rightly been turned away by those nations. Britain must take exactly the same stance," said Freer in a statement.