A man has been arrested in possession of a knife near Buckingham Palace.
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.
A police van arrived with lights flashing and drove him away.
A spokeswoman for the Metropolitan Police said the incident is not believed to be terror-related.
She added: “A man has been arrested in The Mall, SW1, in possession of a knife.
“Patrolling officers detained and arrested the man in The Mall at about 10.40am this morning.
“No-one was injured in the incident and a knife was recovered.
“The man has been taken to a central London police station.”
The arrest happened shortly before the Queen was driven from the palace for an engagement with the Duke of Edinburgh at St Paul’s Cathedral.
They are attending a service to mark the centenary of the Order of the British Empire.
More to follow.