The two tunnel boring machines that will excavate the twin-bore tunnels for London Underground’s Northern line extension have been lowered into the ground.

When tunnelling work begins next month, the two TBMs will begin a 3.2km journey from Battersea Power Station to Kennington, via Nine Elms.

The new link will extend the Charing Cross branch of the Northern line and connect a new mixed-use development at Battersea Power Station to the Tube network.

The TBMs have been named Helen and Amy after Helen Sharman, Britain’s first astronaut, and Amy Johnson, the first woman to fly solo from Britain to Australia.

Transport for London estimates that around 300,000 tonnes of spoil will be excavated for the project. Like with Crossrail, the earth will be transported from site by barge along the River Thames.

The Northern line extension is expected to be completed in 2020.