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 condemned that delay, saying it could mean the vital improvements to the route delay wont be ready by the deadline of 2018.
Political Correspondent Simon Harris reports.
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Pictures of today's events unfolding following a major security incident at the Houses of Parliament.
At least two people have died after a knifeman brought terror to the heart of Westminster.
The Cobra committee brings together government ministers with senior officials of the emergency services and security agencies.