The largest fleet upgrade in a generation is being promised by rail operator FirstGroup as it won the right to continue operating the First Great Western franchise until 2019.
Additional and more frequent services using faster trains with free Wi-Fi will cut journey times from London to Oxford, Bristol, South Wales and Devon and Cornwall.
Key commuter routes, including Bristol, Exeter, Oxford and Gatwick, will see increased capacity in addition to 16% more peak time seats into and out of London Paddington station.
Around 3 million additional seats a year are to be added to the network by 2018.
The rail operator is to introduce Hitachi’s Intercity Express trains into service between London, Bristol and South Wales and the Cotswolds from summer 2017.
A £50 million investment is planned to improve stations and car parks, introducing 2,000 more car parking spaces.
Faster trains will run between South Wales, Bristol and London, with journey times between London and Bristol Temple Meads of 79 minutes and cutting times to Cardiff by up to 14 minutes.
More direct trains will run into Devon and Cornwall, reducing journey times between Paddington and Penzance by up to 14 minutes.
FirstGroup chief executive Tim O’Toole said: “We are delighted to be awarded the contract by the Department for Transport to operate the Great Western franchise to at least 1 April 2019, in a deal that will deliver for passengers and taxpayers.
“As the proud operators of this important franchise, we will be using our unrivalled knowledge and experience of the network to help deliver significant upgrades over the next few years, in particular the introduction of new trains as the mainline is electrified.
“We are already working closely with the DfT and Network Rail to deliver the initial phases of the £7.5 billion Great Western Mainline modernisation programme.
“This investment is the biggest on the route since Brunel, and will transform a key part of the country’s transport infrastructure.
“Under our experienced management, the franchise will see new or refurbished trains on every part of the network, resulting in more frequent and faster journeys and an increase in the number of seats.”
Transport secretary Patrick McLoughlin said: “I am determined that passengers in the West, Thames Valley and South Wales get a railway that is fit for the 21st century.
“This is a fantastic deal which will give them more seats, more services and brand new fleets of modern trains.”