The £22m contract will also see O’Rourke provide additional sidings at Wembley to accommodate longer, five-car London Overground trains.

The deal will support an ongoing £320m capacity improvement and station enhancement programme by TfL.

TfL’s Director of London Overground, Mike Stubbs, said: “This is a key contract in the development of the network as we work to provide 25 per cent more capacity as part of TfL’s continued investment in London Overground.

“It will ensure we remain able to meet the growing demand for London Overground services which – at 89 per cent – have one of the highest levels of passenger satisfaction in London and the South East.”

Work at the Willesden Junction depot includes civil engineering, track, overhead line and third rail electrification and signalling upgrades.

The work will be carried out between March 2014 and March 2015