It follows a campaign by commuters for a later rush hour service in the evening to help ease overcrowding.
Other Thames Valley services will have more carriages with first class compartments converted for use by standard ticket holders. There are also extra trains between Swindon and Westbury.
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Amanda Houston has the lunchtime forecast for the west of the ITV Meridian Meridian region.
Amanda Houston has the lunchtime forecast for the east of the region.
The latest weather forecast for the west of the region from Amanda Houston.