A £900m train order that once looked destined for Germany has been won by the Bombardier plant in Derby.
FirstGroup and MTR have placed the £895 million deal, which is created to provide 46% additional capacity at peak time.
"That agreement also holds good regardless of the new fleet procurement and the announcement on the new trains by the company today".
The order for 750 Aventra carriages, similar to the trains being built for Crossrail's Elizabeth Line and parts of the London Overground, is a boost to the Derby plant, whose future recently appeared in jeopardy.
The new trains should improve journeys for passengers with the introduction of free Wi-Fi, charging points at seats, air conditioning and wide gangways and doors to help make it easier to get on and off the train.
The new trains will start to come into service from mid-2019 and will all be in place by December 2020.
The change of direction for South West highlights a transformation in the rolling stock market, with new trains becoming cheaper to buy than leasing older ones from the banks that own them.
The FirstGroup and MTR partnership will begin running the new franchise on August 20, replacing Stagecoach.
"We know from listening to passengers and stakeholders that, alongside improved performance, what they want to see is additional seats and we will deliver this via these state-of-the-art trains".
Transport minister Paul Maynard said: "This multi-million pound investment in a new fleet of British-built trains is excellent news for South Western passengers and the British economy".
Richard Hunter, Bombardier's United Kingdom managing director, said: "We are thrilled to have won this important contract".