Two men were tackled to the ground by police officers outside Westminster Abbey ahead of the Queen and other royals arriving at the Commonwealth Day Service.
The pair were stopped by police after running into the road outside the central London church.
Pictures show one man being pinned to the ground by five officers, while another is seen being held down nearby by two officers.
Police said they arrested two men for allegedly breaching anti-terrorism road traffic regulations. Both remain in police custody.
The Queen is among those attending the annual service and will be joined by other members of the royal family.
Harry and Meghan are also in attendance, as part of their last event before stepping down as senior royals.
It came as a group of protesters scuffled with police officers outside Westminster Abbey.
The group could be seen holding placards, which read: "#Stop the colonization of former British Cameroons."
The televised service at the abbey is also a key annual event in the calendar for the Queen who is head of the Commonwealth.
