Some 19 protestors were arrested over plans to disrupt the Epsom Derby, one of the largest horse races in the UK.
All of them are being held on suspicion of conspiracy to commit public nuisance.
Police have said they will not not tolerate any risk to public safety ahead of the Classic at Epsom this afternoon.
Activists from Animal Rising had pledged to shut down or delay the derby over fears for the horses' safety, even though there's an injunction banning people from the racetrack.
“Anyone that does break that injunction could potentially face a fine or even imprisonment,” Sky reporter Becky Cotteril said. “[But] I think they will feel any criminal repercussions are worth the risk if it means they can get that message out there.”
Animal Rising member Orla Coghlan said the protestors were not trying to attack any jockeys or horse owners.
“I absolutely don't doubt that the owners and the jockeys love their horses,” she said. “I'm not questioning that at all.”
“But I think that our actions are really not in line with our values.”
Ms Coglan said the British public would support any plans for protesting the horse race in Surrey.
“We know that the British public are on our side,” she said. “I think that we are taking action and representing a really big group of people here,” she said.
Animal Rising previously protested the Grand National, where three racehorses died.
Police arrested 118 people following protests that saw campaigners getting on to the course at Aintree and gluing themselves to the jumps.