The son of veteran campaigner Dan Hooper, better known as Swampy, has become the fourth person to leave the HS2 protest tunnel at Euston, according to HS2 Rebellion.
HS2 confirmed a boy was taken out of a tunnel in Euston Square Gardens on a stretcher “for his own wellbeing”.
Earlier this month Swampy faced criticism when it emerged his 16 year old son Rory was with him in the tunnel complex. But Swampy told ITV News he would not put his son in harm's way.
Rory said in a statement: “After almost three weeks underground I am coming up. This means there will be more food for the others so they can resist for longer.”
He added: “I am looking forward to seeing mum. I have loved digging and being underground and I will continue to protest, HS2 needs to be stopped.
“Young people like me have to take action to stop the ecocide being committed by projects like HS2 because we’re in an ecological emergency and our future is at stake.
“Digging a tunnel may seem extreme but maybe it is the only way.”
The protesters last week lost a High Court bid to block an operation to remove them.
An HS2 spokeswoman said: “The safety of those trespassing and that of the HS2 staff and emergency service personnel in this operation is of paramount importance.
“We continue to do all we can to end this illegal action safely, and we reiterate our message to those underground to comply with the court order and exit the tunnel immediately – for their own safety and that of the HS2 staff, agents and emergency service personnel involved in this operation.”