Twelve people have been arrested on suspicion of criminal damage after activists calling for an arms embargo on Israel sprayed Labour’s headquarters with red paint.

Demonstrators from the Youth Demand group insisted both the Government and Opposition should commit to preventing the supply of weapons to the country as they targeted the party’s offices in central London.

Labour has said arms exports to Israel should be suspended if ministers have received legal advice that it has breached international law, but has resisted backing an embargo without seeing the guidance.

The Government has come under increased pressure in recent days to publish the advice it has been given following an attack which killed seven aid workers in Gaza, including three Britons.

Youth Demand, which is calling for an arms embargo as well as an end to oil and gas drilling in the North Sea, said three of its supporters had sprayed the outside of Labour’s head office while another painted the lobby.

Scotland Yard said officers were called to an incident in Rushworth Street at 2.18pm and arrived within two minutes, arresting 12 people on suspicion of criminal damage.

Labour declined to comment.