Journeys to and from South Wales will be disrupted from the 23rd May to 9th June due to engineering work.
The Severn Tunnel between Bristol Parkway and Newport will be closed while Network Rail work on the overhead power supply and renew some track.
There will be hourly through trains from Swindon to South Wales but they will operate via Gloucester rather than Bristol Parkway and take just over half an hour longer. At peak times there will also be services from Swindon to Bristol Parkway – at other times you will need to travel to Temple Meads and change.
More details at GWR.com