The Thameslink project will go ahead and the route will be served by more train carriages, the government announced today.
The Brighton to Bedford route via London Bridge, Blackfriars and King’s Cross looked to be at risk from the Conservative and Liberal Democrat coalition’s spending cuts.
But Transport Secretary Philip Hammond has confirmed that it will go ahead in full.
The project, however, is not now expected to be completed until 2018, two years later than the current completion date.
The delay is expected to lead to a cut in the cost of the engineering work and to mean fewer journeys will be interrupted while work takes place.
About 1,200 extra carriages are likely to be bought for use on the Thameslink route, which is currently operated by First Capital Connect.
It could be up to eight years before they are all in service.
The project will double capacity on the route to up to 24 trains an hour.
The announcement is part of an £8 billion package of investment in Britain’s railways.
Bob Crow, general secrtary of the RMT rail union, said: “The reality is that the inflation-busting fare increases kick in within weeks while the infrastructure and upgrade works we need to drag the UK’s railways out of the slow lane are light years away.”