Tunnelling to extend the Tube’s Northern line to Battersea will begin in March, the Mayor of London has announced.

A pair of two-mile tunnels will be built to bring two stations to the largely residential area in the borough.

It is estimated the project, the first major expansion of the London Underground since the Jubilee line in the late 1990s, will cost £1.2 billion.

The stations will open in 2020, one at the Battersea Power Station redevelopment and another at Nine Elms that will serve developments such as the New Covent Garden Market, the US Embassy and existing communities.

Mayor of London Sadiq Khan said the expansion of the line to Nine Elms and Battersea will “be a real boost to south London” and the improved transport link will help “to provide thousands of homes and jobs for Londoners”.

He added: "I'm also delighted that local schoolchildren have chosen two such inspirational British women as the names for these tunnelling machines."

Two 650-tonne tunnel boring machines were unveiled on Friday January 20, and due to tunnelling tradition cannot be used until they are named.

To address this, local school children have voted and chose Amy and Helen for the 100 metre-long machines.

The names were chosen to honour the first British astronaut, Helen Sharman, and British aviation pioneer, Amy Johnson, the first female pilot to fly alone from Britain to Australia.

London Underground managing director Mark Wild said: "This is a historic moment for (the tube) as we prepare to start tunnelling to create the first extension to our iconic network for nearly two decades.

"The Northern line extension will bring Battersea and surrounding areas to within 15 minutes of the West End and the City.

"It will also help us to support jobs, homes and growth in this part of south London, help keep pace with the capital's rapidly rising population, and is creating jobs through the supply chain across the UK."