The security alert, reportedly sparked by a letter sent to a peer containing white powder, lasted for an hour and a half before police declared the incident over.
“The incident has been stood down. It was a suspicious package that had been delivered to the Houses of Parliament,” a spokeswoman for the Metropolitan Police told AFP.
“There are no reports of any injuries or illnesses.”
A Lords spokesman had told AFP earlier that parts of the building, including the car park and terrace overlooking the River Thames, were closed “due to a potential security issue that is being investigated”.
He later said: “It’s over. The investigation found that there wasn’t any security threat and so the closed areas were re-opened.”
Matt Chorley, a reporter for The Times newspaper who was on the terrace at the time, had tweeted that police were investigating a “chemical incident”.
“Letter to a peer being analysed by police over white powder in envelope,” he said. Neither police nor the House of Lords would immediately confirm his account.