Transport for London (TfL) has appointed Cleshar as the contractor to lengthen platforms on various overground stations.

Longer platforms are needed to support bigger trains, which will have five carriages instead of four.

The improvements are part of the wider London Overground Capacity Improvement Programme, which will cost £320 million. To meet growing demand on the rail system in the city, the upgrade will provide an increase of 25 per cent. Other changes include signalling and power improvements, as well as stabling - additional track where trains can wait off the main rail in certain areas.

It is expected these changes will help London Overground cope with growing demand. Jonathan Fox, director of rail for TfL, claimed improvements are needed as "passenger numbers by 87 million in its first four years of existence", while 810,000 residents are expected to move into London by 2021.

Similar improvements have also been announced at Waterloo station, helping to improve more stations across London's rail network.

Platforms being extended are mainly on the east London and south London lines. This includes Clapham High Street, Shoreditch and Wandsworth High Street stations. Work is expected to start in the autumn.