Specialist police officers were called to the Palace of Westminster on Tuesday after a letter containing white powder was delivered to an office.
Officers were called at 11.36am following reports that a “suspicious package” had been found.
A heavy police presence was seen on a Ministerial corridor in the House of Commons.
An unnamed police officer in Speaker’s Court told the Press Association: “We haven’t been told much but a package has been left... It won’t be anything to worry about.”
The Metropolitan Police Service said that the office the package was delivered to remains closed at this time.
The rest of Parliament remains open.
Detectives from the Met’s Counter Terrorism Command have been informed and are investigating.
Parliament is currently in recess, meaning that many MPs will not be in Westminster.