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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Sunday's weather update for the east
Sunday's weather update for the west
Philippa has Sunday's weather for the east of the region