The North London Route Improvement Plan will increase capacity and ease current congestion levels.

Secretary of State for Transport Geoff Hoon said: "We are increasing the capacity of this line because we want to make it easier for companies to transport goods across the country by rail, which will ultimately mean there are fewer trucks and lorries on the UK's roads.

"Passengers will also benefit because services will be better equipped to cope in the event of unexpected disruption or planned engineering works.

"It will also spread the load on the network preventing bottlenecks." The project, which also includes improvements to signalling and track layout, will start in 2012 after the London Olympics and will be completed in 2014.