Police investigated reports of a suspicious package this morning in the Parliamentary office of Lib Dem leader Jo Swinson.
Officers were alerted to the package just before 10am on Monday in Portcullis House in the highly-guarded Palace of Westminster.
Multiple sources said it affected Ms Swinson's office. The office and some staff were thought to have been quarantined while police carried out checks.
Police were stationed on the third floor telling staffers to turn back but the building was not evacuated. Just after noon, Scotland Yard confirmed the package "has now been assessed as non-suspicious."
It is thought Ms Swinson was not present at the time.
NHS ambulances and an Incident Response Unit were seen on Whitehall outside the nearby Derby Gate entrance to Parliament.
A Met Police spokeswoman said earlier: "Police were called at approximately 09:51hrs on Monday, 4 November to reports of a suspicious package delivered to Portcullis House, Westminster.
"Officers are in attendance and the contents of the package are being assessed.
"No reports of any illness or injuries.
"The premises have not been evacuated. Enquiries continue."
A House of Commons spokeswoman confirmed: "We are aware of an incident on the Parliamentary Estate which is being managed by the police."
Packages delivered to Parliament are security screened and scares over suspicious parcels are not uncommon.
But it comes amid a backdrop of rising threats against MPs ahead of the December 12 general election.
Politicians have been told to take unprecedented security precautions, with some telling The Observer they have been advised not to campaign alone or after dark.
