The project will involve improving capacity across the East London Line and North London Lines through platform extensions, station modifications and depot reconfigurations.

Sweett has previously been involved in the East London Line Phase 1a and Phase 2 projects, the latter of which is due to come into operation in December 2012.

Eryl Evans, director with responsibility for the group’s UK transport work, said: “Working with major transport operators such as TfL gives us the opportunity to help improve the efficiency of London Overground’s operations, ensuring that investments in infrastructure provide an improved travel experience and value for money for London residents.”

Derek Pitcher, managing director of Europe, said: “We continue to make significant investments in developing our capability across the UK infrastructure sectors, which is now resulting in high-profile framework appointments across both the public and private sectors.”