Scotland Yard said they were informed about the suspicious package that had been delivered to an office within the Palace of Westminster this morning, days after a Russian spy was allegedly poisoned with a deadly nerve agent.
The package was later described as a letter which contained a white powder, which has been assessed by specialists and found not to be noxious, the Metropolitan Police said.
Detectives from the Met's Counter Terrorism Command have been informed and are investigating, the statement said.
"We are aware of a potential situation involving a suspicious substance which the Met Police are investigating. There has been no evacuation, but the affected area has been cordoned off. Access to the building is otherwise unaffected. We cannot provide any more details at this stage," a parliamentary spokesperson said.
More From This Section
London Ambulance Service said it had attended the scene and taken a man and a woman to a nearby hospital as precaution.
The incident comes days after a Russian spy was allegedly poisoned with a deadly nerve agent.
Skripal and Yulia remain in a serious condition along with a police officer who came in contact with the same substance.
Last month, UK home secretary Amber Rudd had white powder sent to her office in Parliament which was also assessed and found to be not dangerous. Rudd was not in the country at the time.