Climate protesters have occupied a tunnel in a bid to save trees from being cut down to make way for new housing.
Police and bailiffs have attempted to evict activists from the site of the demonstration near a busy roundabout on Highbury Corner, in Islington.
Protesters at the Highbury Corner Protection Camp said bailiffs arrived "acting under instructions from Islington Council" and discovered the tunnel, which had been "cunningly concealed within a pallet stronghold, fortified with earth from the tunnel itself".
One campaigner in the tunnel named Maria said: "Our governments, local and national, are out of touch and not representing the people. They declare a climate and environment emergency and then carry on destroying trees and countryside. It's got to stop."
The Metropolitan Police said officers attended the site to assist Islington Council with the enforcement of a High Court writ.
A spokesperson said: "One man has been arrested for obstructing a high court enforcement officer an one fixed penalty notice has been issued for breaching COVID regulations."
A police presence remains in the area to "prevent further potential breaches of the peace and to uphold COVID legislation"
The group has been living on the site for almost four months to try and save seven mature trees due to be felled to allow for the construction of a six-storey block of housing.
Executive member for housing and development at Islington Council, Diarmaid Ward, said the new development would result in 25 "desperately needed" new council homes.
He added: "At the same time, the project will deliver 63 new trees, an extra 100 square metres of communal garden space for residents, and a number of plantings and landscaping improvements designed to improve biodiversity and address air quality issues."
Mr Ward said the council had reached an agreement with an initial group of XR protesters to avoid taking legal action, which meant if they left the site voluntarily the council would use the money it would have spent on legal fees on additional trees.
"We have given protesters who chose to remain every opportunity to comply with the directions of the court, including additional time," he said.
"It's truly disheartening that people who claim to care about both trees and homes have forced an outcome resulting in fewer trees for the borough, significant costs, and further delays to building much-need council homes for local families in desperate need."
Another group of protesters have also occupied an extensive 100ft underground network beneath Euston Gardens to try and stop the development of HS2.
Demonstrators at Highbury Corner say their tunnel was built by the same group, but is not part of the anti-HS2 campaign.