GWR signed a contract with Porterbrook Leasing earlier this year to lease 37 class 387s in addition to the eight trains it had already ordered for Thames Valley services from Paddington to Reading, Oxford, and Newbury. The EMUs will gradually extend their range as further phases of the troubled Great Western electrification programme are completed, enabling the redeployment of class 165/166 Turbo DMUs elsewhere on the GWR network.

The class 387s will initially operate two morning and two evening return trips between Paddington Hayes & Harlington running in eight-car formations.