Anti-HS2 protesters say efforts to evict them from tunnels under a small central London park are “dangerous” as they prepare to spend a sixth night underground.

Environmental campaigners have dug a network of tunnels beneath Euston Square Gardens, next to Euston station, in a bid to protect the green space which they claim will be built over with a temporary taxi rank before being sold to developers as part of plans for the high-speed railway.

A spokesman for HS2 Rebellion, an alliance of groups and individuals campaigning against HS2, said bailiffs were “digging constantly” as part of attempts to remove activists from the fenced-off site.

HS2 Ltd said it has “legal possession” of the land and urged protesters to leave “for their own safety” before they are removed by High Court enforcement officers.

But John Cooper QC, representing the protesters, tweeted on Monday afternoon: “We have just issued Judicial Review and urgent injunction applications on behalf of our clients.”

In an order issued on Monday evening, High Court judge Mr Justice Robin Knowles refused an application brought by Larch Maxey, one of the activists in the tunnels, for an injunction requiring HS2 and others to cease operations.

The order says Dr Maxey should “until further order… cease any further tunnelling activity and is not to cause any other person to engage in tunnelling”.

He should also inform HS2, the Health and Safety Executive, London Fire Brigade, or the police, how many people are in the tunnels, details of any children, give details of the “layout, size and engineering” used for the tunnels and co-operate with the agencies involved “to leave the tunnel safely and allow others to do the same”.

The order says where there is a safe method of doing so, Dr Maxey should have “reasonable access” to his lawyers, and that in taking decisions, HS2 should “(continue to) consider carefully”, with the HSE and the fire brigade, the opinions of Dr Maxey’s expert witness.

The judge’s order notes the situation Dr Maxey is in “is very dangerous”.

Earlier on Monday, the protest group shared two clips apparently filmed by activists underground.

In one, a protester confronts a man in a helmet, face mask and wearing a head torch, about digging a “parallel tunnel” on the other side of a metal grille.

She says: “I’m aware that’s very risky for health and safety, major health and safety breaches parallel tunnels.”

The man replies: “I didn’t realise you have a tunnelling qualification to your name actually. Well I have, thank you, and I know exactly what I’m doing.”

The activist says: “Since you started digging the ceilings are starting to go, so can you tell me why you’re engaging in dangerous practices?”

In another clip, an unnamed male protester says campaigners are having a “great time” in the tunnels, with games and books to fill the time.

He adds: “But this side shaft that they are digging is real dangerous.”

Earlier on Monday, Dr Maxey, speaking to the PA news agency by phone from the tunnels, said: “Conditions are good.

“They are warm. They are a bit moist, there’s a little bit of water coming in, but it’s not too bad.

“Our spirit is really good, we’re all working really well together and really grateful to take this stand.”

HS2 Rebellion confirmed there were nine activists in the tunnels, including Dr Maxey, 18-year-old Blue Sandford, and individuals named as “Digger Down” and “Lazer”.

They also included veteran environmental campaigner Swampy, real name Daniel Hooper, and his son Rory.

Dr Maxey, 48, a former geography lecturer and post-doctoral researcher, claimed efforts to evict the group were “unlawful”.

He said: “It’s an unlawful eviction and it’s being carried out in an unlawful way because they are not following safety protocols and the due process, making sure it’s safe for everyone.”

An HS2 Ltd spokeswoman said the Health and Safety Executive (HSE) had reviewed the operations to remove the activists safely and had “made no immediate observations during the visit as to improvements we need to make”.

“The safety of people trespassing and the safety of HS2 staff and agents in this operation is of paramount importance,” HS2 Ltd said in a statement.

“We are doing all we can to end this illegal action quickly and safely, including providing those underground with air – despite claims to the contrary.

“HS2 has legal possession of this land, therefore the High Court enforcement officers are lawfully empowered to remove illegal trespassers using minimum force at this time. Our message is however that those in the tunnels should come out now for their own safety.

“It is forecast to rain regularly over the next 48 hours and we have repeatedly raised concerns to the activists that their crude tunnels are simply not equipped to deal with these weather conditions.

“If the reports are accurate and there is also at least one minor stuck underground, we firmly reiterate our message: please, come out from the tunnels immediately, and stop putting your lives, the lives of children and those of the emergency services at risk.”

An HSE spokesman said: “HSE is aware of the protest and is in liaison with HS2 in order to review any plans that would affect workers, protesters or rescue personnel.”

On Monday it was announced that HS2 Ltd chairman Allan Cook had handed in his resignation and will leave in July rather than December as originally planned.

A Department for Transport spokesman insisted his decision was not linked to the protest and Mr Cook’s letter of resignation said his decision would enable his successor to focus on the “future momentum of the project”.