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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Dry and sunny tomorrow and feeling warm.
Mild tonight with warm sunny spells and light winds tomorrow.
A section of the M3 has been closed and bomb disposal units are at the scene after reports of "potential hazardous material in the road".