The quintet have been at the site in Harvil Road since yesterday but were 'evicted', according to campaign group Stop HS2.
Police, bailiffs and a series of protestors have been at the scene today.
One protestor, Sarah Green, got on to the site yesterday at approximately 10am, and she was then joined by four other campaigners at around 7pm last night, according to Mark Keir from the Hillingdon Green Party.
The campaigners are protesting about the high-speed rail link, HS2, which will connect London to Birmingham and Manchester.
HS2 trains will pass through Ruislip and Harefield when the railway is operational, with the Hillingdon Outdoor Activity Centre in Harvil Road set to close as a result.
Work in Harvil Road started yesterday morning and the site is part of the early works programme which prepares ‘the route for the construction of the railway’, according to HS2. Signs advertising the works have been present on Harvil Road for the last couple of weeks.
Mr Keir from the Hillingdon Green Party said HS2 will destroy the Colne Valley, which surrounds the site in Harvil Road, affecting various species of animals.
He said: “Sarah got into the compound yesterday at about 9/10 o’clock and found a way to get under the digger. She had a scout around and saw a huge amount of destruction. She has been a long-time campaigner against HS2 and she knows about the nature and the environmental stuff and the habitat loss that this represents. She got under the digger to stop things and say we’ve got to stop it and we want something different.
“Behind me is the Colne Valley and it’s a huge checker board of habitats which are all wonderfully linked up. There are over 2500 species which live there. There are 13 species of Bats, 120 species of Birds which nest here and just recently there was an Osprey sighted feeding.
“It also represents a huge piece of natural sub defense for the whole of Hillingdon and Uxbridge and goes all of the way down to Staines. The Colne Valley is a wonderful piece of biodiversity and will be trashed.”
Protestor Liz Williams said: “HS2 is going to decimate the local area. It’s an environmental disaster to this country and is going to destroy thousands of acres of natural land for no reason.”
She added: “This is the beginning of direct action because we have been fighting this for seven years now.
“We’ve been through all the legal channels, we’ve been peaceful and law abiding and we’ve been doing everything we can to get the country and government to listen to us. But they won’t. So, more of this is going to happen.”
A HS2 spokesperson said earlier today: “There is an ongoing incident at an HS2 site at Harvil Road. The safety of everyone involved is our top priority. We have ownership of the land and all necessary permissions to undertake works on the site.”
The first phase of the railway, which connects London to Birmingham, is due to open in December 2026.
Trains will travel at up to 250 mph and will enable passengers to travel from London to Birmingham in 49 minutes, the project's creators say.