Four and a half billion pounds will be spent on 600 carriages for the routes from Paddington to Reading, Newbury, Swindon, Oxford and Banbury.
It should lead to major improvements in the Thames Valley.
But a row has broken out about the contract being awarded to a Japenese company.
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More than 900 jobs will be created and thousands more secured after Transport Secretary Justine Greening approved a £4.5bn contract to supply Britain with the next generation of intercity trains.
Meridian Tonight can exclusively reveal that a one billion pounds worth of Japanese Bullet trains will be used in the Thames Valley. First Great Western hopes the first of the 500 carriages will come into service in 2016.
Our Transport Correspondent Mike Pearse was given exclusive access to the Hitachi factory in Kasado which is close to Hiroshima and to ride on the world famous Shinkansen bullet trains.
In this report he talks to Kentaro Masai of the Kasado factory and Darren Cumner who will be in charge of the assembly plant in the UK for the trains.
Meridian exclusively can reveal the Government will announce an order for one billion pounds worth of new Japanese style bullet trains within the next week for First Great Western services in the Thames Valley.
500 new carriages will be built with the first in operation around 2016 or 2017, our Transport Correspondent Mike Pearse understands.
The new trains will not look quite like the latest Shinkansen bullet trains but they will have the same technology. The latest ones in Japan have a very long nose which helps with the aerodynamics. The ones here will be shorter but will be distinctive.