Four people have been arrested after they broke into Silverstone for Sunday's British Grand Prix.
The detained, understood to be associated with the environmental group Extinction Rebellion, were dressed in marshals uniforms.
They unfurled a banner with the message, "Act Now", at Club Corner ahead of the race before they were stopped by track security.
A joint statement issued by Silverstone and Northamptonshire Police following Sunday's grand prix read: "During the race, Northamptonshire Police were made aware of four people who had been detained by Silverstone security inside the venue perimeter.
"Officers are working closely with Silverstone Circuit and conducting a full investigation. Four people have been arrested and are in police custody."
The incident will be a concern for Formula One's bosses, with Sunday's race taking place behind closed doors due to the Covid-19 pandemic.
The 70th Anniversary Grand Prix will also be staged here at Silverstone next weekend.
Sunday's incident is not the first time the Silverstone race has been targeted by protesters.
A safety car was deployed in 2003 after an intruder ran across the 200mph (320kmph) Hangar Straight.