The work will create two 3.2km underground tunnels that will extend the Charing Cross branch of the line from Kennington to Battersea, via Nine Elms.

It is expected that the extension will support the creation of 25,000 new jobs and more than 20,000 new homes, as well as regenerating the areas of Vauxhall, Nine Elms and Battersea.

Two of the constructed stations will link the Battersea Power Station and Nine Elms developments.

A pair of 650-tonne tunnel-boring machines will be used to excavate the tunnel and have been named Helen and Amy by local schoolchildren.

The names pay tribute to the first British astronaut Helen Sharman, and the first female pilot to fly solo from Britain to Australia, Amy Johnson.

The machines will tunnel at depth of 26m for six months and remove an estimated 300,000 tonnes of earth.

Mr Khan said: “It’s great news that we are going to begin tunnelling for the Northern Line Extension. 

“Extending the line to Nine Elms and Battersea is going to be a real boost to south London, with the improved transport link helping to provide thousands of homes and jobs for Londoners.

“I’m also delighted that local schoolchildren have chosen two such inspirational British women as the names for these tunnelling machines.”