Extinction Rebellion activists have locked themselves to a drilling rig in the Thames at North Greenwich to halt preparatory work for the Silvertown Tunnel.

Activists boarded the structure early this morning, which they say is being used to place "seismic monitors" ahead of drilling the main borehole for the tunnel next year, sending the lock keys to Mayor Sadiq Khan.

The £1.2 billion project, which will link Silvertown and Greenwich Peninsula, has been a longstanding point of controversy, with opponents claiming it is incompatible with environmental aims.

A spokesperson from the Extinction Rebellion affinity group responsible for the action said: “All legitimate means of stopping this tunnel have been tried.

"We have been working with the Stop the Silvertown Tunnel coalition for the last 2 years engaging with councils and MPs drawing up petitions, raising awareness, staging protests and pleading with Sadiq Khan.

"Being an asthma sufferer himself and claiming to be committed to cleaning London’s air we hoped that he would have listened to us, however we can’t compete with the lobbying power of London city airport and the canary wharf group.

"Extinction rebellion are committed to doing everything in our power to fight the climate crisis and the social injustice that accompanies it.

"We will fight this tunnel with non-violent direct action every step of the way.

"The keys to the locks which the activists have been secured to the rig with have been delivered to Sadiq khan, he is the only person with the power to stop this and yet he has repeatedly failed to respond to the points we have raised."

In a separate protest, activists dressed in white costume were seen marching around Greenwich Peninsula. 

Opposition group Stop the Silvertown Tunnel argues the project undermines the Mayor's own 2030 carbon neutrality target, and his goal of increasing cycling and walking in the capital.

The group has also raised concerns the tunnel would bring more traffic and pollution to the 80 per cent black and minority area of Newham, which already struggles with air quality issues.

A multi-national consortium successfully bid for the contract from Transport for London in November.

Riverlinx will chip in private capital to fund the project, receiving repayment via a vehicle toll on the tunnel in a private finance initiative (PFI).

The Mayor’s office has said introducing tolls at Blackwall and Silvertown tunnels would “play a crucial role in tackling congestion, improving overall air quality and providing much-needed additional bus services across the river".