GWR has urged customers “to only travel if absolutely necessary” between London Paddington, Bristol and South Wales on Sunday.

There will be fewer services, which will stop at Reading, but a diversion will be in place adding about 30 minutes to journeys. Anyone still wanting to travel “must make a reservation”.

It also said that due to the late notice of some of the engineering work, journey planners would not be fully correct until they are updated overnight on Saturday.

A full list of the routes affected by the works can be found here, external.

GWR said there would be reduced services to and from London Paddington throughout November and early December and apologised for the disruption.

Network Rail’s Western route director Marcus Jones said their work to improve the performance of the Thames Valley line was “well under way”.

He said they were upgrading drainage systems and the track which was “essential” to the goal of reducing disruption and improving the resilience of the line.