Counter-terrorism officers were deployed to investigate the substance amid increased security just one day after the US President’s daughter-in-law was taken to hospital after opening mail containing a white powder.
The Home Secretary is currently in the United States, but her staff received the package at her office today and said they were “thrown into a panic”.
The Metropolitan Police confirmed they had been alerted to a suspicious package delivered to the Palace of Westminster.
A statement from the Met Police said: “At approximately 11.36am on Tuesday, 13 February, police were informed of a suspicious package that had been delivered to an office within the Palace of Westminster. Police are at the scene and dealing.
“The letter contained a white powder which is currently being assessed by specialists.
“The office remains closed at this time, but the rest of the Palace of Westminster is open.
“Detectives from the Met’s Counter Terrorism Command have been informed and are investigating.”
Staff were forced to evacuate as police swooped to investigate.
A House of Commons spokesman later confirmed the powder on the Parliamentary Estate was found to be “non-harmful”.
No extra officers were present at the Palace of Westminster today, but a security message was displayed on the screens in some of the buildings, saying: “Incident in the house of Commons being dealt with by the Metropolitan Police. Do not be alarmed.”
Witnesses had earlier said police had told them they were dealing with a “suspicious package”, which was confirmed by an unnamed officer.
He said: “We haven’t been told much, but a package has been left. Specialist officers have just arrived to examine it. It won’t be anything to worry about.”
Parliament is currently on recess so most MPs are not in Westminster this week.
Last year five people were killed when a terrorist carried out an attack on Westminster Bridge and in the grounds of Parliament.
Four pedestrians were killed when they were struck by Khalid Masood before PC Keith Palmer was stabbed to death as he protected Parliament and presented the killer from entering.
The alert comes one day after Donald Trump’s daughter-in-law was rushed to a New York hospital after she opened a piece of mail containing an unidentified white powder that was later determined to be non-hazardous, officials said.
Vanessa Trump, the wife of the president’s eldest son Donald Jr, was hospitalized after she complained of nausea following her exposure, New York officials said. Two other people who were present were also taken to the hospital.
US authorities have been on alert for mail containing white powder since 2001, when envelopes laced with anthrax were sent to media outlets and US lawmakers, killing five people.