A major milestone has been reached on the £1.2 billion Northern Line Extension project in London.

Two tunnel boring machines (Helen and Amy) have been lowered 20 metres below ground in Battersea.

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

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Each machine will be assembled within two 77 metre long launch tunnels before starting work towards Kennington next month.

After both tunnel boring machines and their gantries are built, a conveyor system will be developed to take the spoil from the tunnels up to barges on the River Thames. More than 300,000 tonnes of earth will be excavated by Helen and Amy in this way before the spoil is taken to Goshems Farm in East Tilbury, Essex by boat where it will be used to create arable farmland.

The tunnelling phase will take six months to complete, while the overall £1.2bn extension is targeted for completion in 2020.

Once finished, the development is expected to help create up to 25,000 new jobs and 20,000 new homes.

(LM)