The pensioner is in a critical condition in hospital after the smash in Earl’s Court, West London this afternoon.
Two bikes – one with King Charles’ cypher – were seen inside the cordon this evening.
The King and Queen are believed to be in Sandringham.
Met Police’s Special Escort Group provide armed escorts for Royal Family members, VIPs, protected members of the Government, visiting royals, heads of state and other visiting dignitaries.
It also provides armed vehicle escorts for valuable, hazardous and protected loads – and can include high-risk prisoners.
A Met Police spokesperson said: “A woman has been injured after being involved in a collision with a police motorcycle in west London.
“At approximately 15:21hrs on Wednesday, 10 May a police motorcycle on escort duties was involved in a collision with a member of the public on the junction of Cromwell Road and Warwick Road, SW5.
“Paramedics from the London Ambulance Service and London’s Air Ambulance attended and a woman, aged in her 80s, has been taken to hospital.
“She remains there in a critical condition. Her family have been informed.
“There are no reports of any other injuries. Enquiries into the circumstances of the collision are ongoing.
“Road closures remain in place while the scene is dealt with.
“As is routine, the Directorate of Professional Standards has been informed.”
Buckingham Palace declined to comment.