Police stormed to to the scene shortly after it was announced that the Changing of the Guard ceremony has been cancelled.

The Palace of Westminster has also been closed.

An eyewitness said he saw a man surrounded by officers and handcuffed as he sat on the ground in The Mall at around 10:40am on Wednesday.

The incident comes less than 48 hours after ISIS suicide bomber Salman Abedi struck Manchester Arena with a bomb during an Ariana Grande concert, killing 22 people and injuring more than 20 others, reports express.co.uk.

A police van, with flashing lights, rushed to the scene and drove him away.

A spokeswoman for the Metropolitan Police said the incident is not believed to be terror-related.