The contractors originally planned to start the main drive last summer, but this was delayed following design changes in the Battersea station box needed to launch the two TBMs.
Progress was held up because the developer of Battersea Station decided to build part of its third phase housing over the box rather than beside it requiring a more robust design.
Work over the next three months includes the creation of two 77m long tunnels to the east of the Battersea Station site, from which the tunnel boring machines will be launched.
The contractors hope to make up for lost time on the tunnel drive keeping the whole project on schedule to open in 2020.
Each of the 650-tonne machines will create two 3.2km underground tunnels to extend the Charing Cross branch of the Northern line from Kennington to Battersea, via Nine Elms.
The machines have been named Helen and Amy by local school children in honour of the first British astronaut, Helen Sharman, and British aviation pioneer Amy Johnson.
The machines will tunnel at depths of 26m 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 arable farmland.
This will remove more than 40,000 lorry journeys from the Capital’s roads, reducing congestion and significantly reducing the site’s carbon footprint.