Police were investigating an incident in the British parliament on Tuesday, the lower house of the legislature said, and media reports said officers were checking a suspect package.
"The police are currently investigating an incident on the parliamentary estate," a House of Commons spokesperson said, without elaborating.
A police spokesman said he was not immediately able to comment.
Britain's parliament is currently in recess.
News website MailOnline and the Press Association news service said the incident involved a suspect package.
A Reuters correspondent in parliament said there was no sign of a broader security alert in the building.
Police have increased security at parliament after an Islamic State-inspired attacker killed five people a year ago by driving a car into pedestrians on Westminster Bridge and then stabbing to death a police officer in the grounds of parliament.