Animal Rising activists plan to scale the fences and enter the track of Aintree Racecourse before the Grand National race begins on Saturday.
The climate and animal rights group said up to 300 activists will attend the venue from 9.30am where they intend to prevent the race from starting.
They will also block traffic by performing a slow march along Ormskirk Road, the main access route.
Nathan McGovern, a spokesperson, said: “We do plan to be periodically blocking Ormskirk Road, the access road to the front of the racecourse, to disrupt the entry to the venue throughout the day.
“The group of people at the front will be peacefully attempting to make their way over perimeter fences/walls at the front of Aintree before the Grand National race begins with the intention of making their way onto the track.
“And all of this is before the race even starts. We will not be entering the track if there are horses and jockeys riding.”
Merseyside Police said they have a “robust policing plan in place” and are working with Aintree’s owners The Jockey Club in preparation for any incidents.
One horse has already died at the Grand National Festival – Envoye Special, ridden by James King – after it fell in the Foxhunters’ Chase just after 4pm on Thursday.
It is the 60th horse to have died at Aintree in the past 23 years.
Animal Rising, which changed its name from Animal Rebellion on Monday to move away from the umbrella of Extinction Rebellion, wants to use UK horseracing’s biggest calendar event to highlight the “broken relationship” between humans and animals.
Mr McGovern said: “It’s a spotlight that we really need to be using to push a national conversation about our broken relationship, not only with horses but with all the animals that we use, whether that’s for food, fun, entertainment and dog and horse racing.
“This is very much about a bigger picture of recognising that, in a nation of animal lovers, we’re not really living up to those values with our actions.”
Animal Rising’s plans for the Grand National first became public when an undercover Mail on Sunday reporter attended a meeting earlier this month.
They said the activists planned to use ladders and bolt cutters to get through Aintree’s perimeter fencing.
A spokesperson for Merseyside Police said: “Merseyside Police has a robust policing plan in place for Aintree, as it does for any major public event, to ensure the safety and wellbeing of everyone involved.
“We have been working with our partners, including The Jockey Club, for a number of months in the build-up to this year’s festival to ensure that any necessary plans and processes are in place to deal with any incidents that may arise and to prevent any significant or ongoing disruption to racegoers and local residents and businesses.
“We respect the right to peaceful protest and expression of views, but public order or criminal offences will not be tolerated and will be dealt with robustly.”
A spokesperson for Aintree Racecourse said: “We respect the right to peaceful protest but sincerely hope that Animal Rising reflect on whether their proposed actions are legitimate and responsible.
“Their actions could endanger the horses they purport to protect, as well as jockeys, officials and themselves.
“As you would expect, we are working closely with Merseyside Police to ensure we protect the safety and enjoyment of everyone, including all participants, human or equine, at the Grand National.”
A spokesperson for the British Horseracing Authority said: “While we respect the rights of anyone to protest safely and legally, we condemn any action which is illegal, especially if it puts at risk the safety of horses, jockeys, officials or fans.”
Shortly before 10.30am, Merseyside Police said a 33-year-old woman had been arrested on suspicion of conspiracy to cause public nuisance in connection with potential co-ordinated disruption activities at Aintree.
The woman, from the London area, was arrested in the Greater Manchester area on Saturday morning, police said.
A force spokeswoman said: “Merseyside Police has been working with The Jockey Club and other partners to keep people safe during the Grand National Festival.
“We are aware of some people planning to protest at the event. This has been factored into our plans. We respect the right to peaceful protest and expression of views, but criminal behaviour and disorder will not be tolerated and will be dealt with robustly.”
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