Great Western Railway will run an amended service on 1st January 2020, details are as follows:
The first train services of the day will start up later than usual on most routes. Trains between London Paddington and Swansea will run between London Paddington and Bristol Parkway and then restart from Cardiff Central. Trains between Bath Spa/Chippenham and London Paddington have a reduced service operating. Trains between Cardiff Central and Portsmouth Harbour will start/terminate at Bristol Parkway instead of Cardiff Central. Trains between Cardiff Central and Taunton will start/terminate at Bristol Parkway instead of Cardiff Central.
Rail replacement buses will operate between Bristol Parkway and Newport (fast, plus calling at Patchway and Severn Tunnel Junction), Bristol Parkway and Cardiff Central (fast) and Newport and Cardiff Central.