One person remains underground after veteran environmental activist Swampy left a network of tunnels in central London where they had been protesting against the HS2 railway line.

Swampy – real name Dan Hooper – was among three people who were arrested after leaving the site in Euston Square Gardens on Thursday morning.

The network of tunnels, discovered on January 26 near Euston station, was created in secret by protesters who object to the redevelopment of the area as part of the high-speed railway line.

HS2 Rebellion, the campaign group behind the protest, said one person still remains in the tunnel despite spending 30 days underground.

I’m going to carry on protesting with everything I have because I’m fighting for the lives of everyone I love. We need you too - please help

Eight campaigners have left the tunnels so far.

Swampy, 18-year-old Blue Sandford, daughter of Scottish landowner Roc Sandford, and an unnamed 22-year-old woman were the latest to voluntarily leave.

They are said to be “well” and in “high spirits”, according to HS2 Rebellion.

Ms Sandford said: “I’m going to carry on protesting with everything I have because I’m fighting for the lives of everyone I love.

“We need you too – please help.”

A Metropolitan Police spokesman confirmed the three had been arrested on suspicion of aggravated trespass.

A statement from the force read: “They were taken to hospital as a precaution and subsequently into custody at a London police station.

“Officers remain at the HS2 site.”

Swampy went into the tunnels alongside his teenage son Rory.

It comes after Larch Maxey, 48, was removed from the site by bailiffs on Monday and handed over to the Met.

The geography lecturer appeared at Highbury Corner Magistrates’ Court on Tuesday where he denied criminal damage and two counts of obstructing or disrupting a person engaged in lawful activity.

A 16-year-old boy who left the site last Wednesday has been bailed to return to a central London police station on a date in mid-March.