Police have detained a woman, said to be in her 40s, after she attempted to drive her red Volkswagen through the House of Commons gates.
The car managed to come within yards of sitting MPs as they voted on a gay marriage bill, despite increased security.
An automated security ramp managed to halt any further progress. Witnesses claim a woman in a red Volkswagen drove through the Carriage Gates and demanded to see an MP before locking the doors of the car at around 7.15pm last night.
Security officers were forced to smash the car window and subsequently arrested the woman for trespass.
A Scotland Yard spokesman told The Evening Standard the woman drove through Carriage Gates at around 7.15pm and was stopped by police.
"Following a brief conversation between officers and the woman she locked herself inside the car and refused to leave," he said.
"A short time later officers broke a window of the car and the woman was arrested for trespass on a designated site.