Transport Secretary Patrick McLoughlin said today is a "very important day" for Derby-based train maker Bombardier.
The firm signed a £180 million deal to provide another 116 carriages for Southern, to be used on services through London.
In 2011, the company lost out to German firm Siemens to build new train carriages for its Thameslink route.
Speaking today Mr McLoughlin said: "I think Bombardier have put it behind then, there was disappointment and I shared that disappointment but there was an open process, an open contract, they didn't win that particular one."
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