Bombardier has been selected to supply 116 new EMUs for train operator Southern.
The new carriages, which are worth £180 million, will operate on the Thameslink route to allow current vehicles to be distributed to newly-electrified lines before themselves making way for the new Siemens-built Thameslink stock.
The order includes an option for 140 more vehicles, giving the contract a potential value of £385 million.
Southern managing director Chris Burchell said: “We have worked extremely hard to be an effective delivery partner to the Department and we are very pleased to have reached this important milestone in the procurement of new rolling stock. This will provide essential capacity to allow our industry to grow.”
The Secretary of State for Transport, Patrick McLoughlin said: “Increasing the number of trains on the network not only benefits passengers but everyone, as the railways are an important engine for economic growth in our country.
“The Government has worked closely with Southern to enable this critical stage of the project to be reached and I look forward to these trains being delivered onto the network.”
There will now be a 10-day cooling off period before the order can be confirmed.