Has the Government's failure to buy new trains for Thameslink put the entire upgrade of the multi-billion pound route at risk?
The Government was supposed to sign a contract for the trains three years ago.
Today the National Audit Office (NAO) condemned that delay, saying it could mean the vital improvements to the route delay wont be ready by the deadline of 2018.
London Bridge station is a building site. It is at the heart of a £6.5 billion project to try to end overcrowding on one of the busiest commuter routes.
Almost a hundred thousand passengers a day travel on Thameslink trains on the Bedford to Brighton line.
But according to a report by the National Audit Office, the ambitious and costly plan to introduce longer trains and more of them could be in trouble.
The rebuilding project is now on track but the Government still has not signed a crucial deal for new trains even though it was supposed to happen three years ago.
That means the railway with smart new stations like Blackfriars might be ready. But the trains will not be.
The project was first conceived as early as 1991, it was given the link Thameslink 2000 in honour of the projected completion date. Now it is 2018 at the earliest, Labour says it is a shambles caused by the incompetence of ministers.
The current Thameslink trains have been in service for twenty five years. For many commuters, the new trains and new timetables can not come soon enough.
The government has been criticised for refusing to award the contract for the new trains to a factory in Derby.
They are expected instead to be built by Siemens of Germany. If a deal can be done.
Ministers admit it is complex but say negotiations are in the final stages.