TWO giant tunnel boring machines have been lowered into place to dig beneath London - and they have been named in honour of two Yorkshire women.
Tradition dictates that huge devices cannot start work until they have been given names.
Following a vote by local schoolchildren they will be known as Helen and Amy.
This is in honour of the first British astronaut, Helen Sharman, of Sheffield, and British aviation pioneer Amy Johnson, of Hull, who was the first female pilot to fly solo from Britain to Australia.
The machines will create a pair of two-mile long tunnels to bring the Tube network to Battersea, in the south of the capital.
Tunnelling to Kennington will begin in March and is expected to take six months.
The £1.2bn project is the first major expansion of the Tube since the Jubilee line in the late 1990s.
Two new stations will be opened in 2020 - one at the heart of the Battersea Power Station redevelopment and another at Nine Elms, serving developments such as the US Embassy and the revamped New Covent Garden Market, as well as existing communities.
The 650-tonne machines are undergoing final testing before commencing work on the tunnels. Each one is capable of tunnelling up to 30 metres per day with teams of around 50 people needed to operate them.
The work is expected to take around six months to complete.
As they advance forward, nearly 20,000 pre-cast concrete segments will be built in rings behind them.
The machines will tunnel at depths of 26 metres for six months, excavating more than 300,000 tonnes of earth. This will then be passed along conveyors before being loaded on to barges and taken to Goshems Farm in East Tilbury, Essex, where it will be used to create farmland. London Underground said the Northern Line Extension will bring Battersea to within 15 minutes of the West End and City.