Rail users are being warned to prepare for major disruptions to all services operating through Trowbridge and Westbury this summer, due to the electrification of the Great Western Mainline.

Electrification of the mainline from London Paddington to Bristol Temple Meads is planned to reach the Wiltshire area during July and August, when work starts on the Chippenham to Bath section.

The section of the mainline most affected will be from Chippenham to Bath, which will be closed in two stages, with stage one planned for July 18-31.

It will mean severe disruption of the line from Chippenham to Bath, while electric cables are strung through Box tunnel.

As a result, those travelling to London via Bath will instead go via Bath, Bristol Temple Meads, Bristol Parkway and the South Wales mainline, via Swindon, or an hourly service from Bath to Chippenham by an alternative route and then onwards to London.

Horace Prickett, passenger transport portfolio holder for Wiltshire Council, said: “The current electrification of the Great Western Mainline from London Paddington to Bristol Temple Meads is the largest project since the war.

“It is due to reach the Wiltshire area during July and August this summer, when rail users will start experiencing major disruptions to all services operating through Trowbridge and Westbury.

“Full details are still being worked out but many services will be replaced by buses which will inevitably mean longer journey times and probably poor connectivity with onward services.

“All of this is yet to be worked out in detail, but it is important that people are aware of considerable disruption from July 18 to August 31, especially if they are expecting to book rail journeys connecting with holiday flights.”

During stage one, the current Bristol to Waterloo service should run as timetabled, as will the Portsmouth to Cardiff, but with some possible delays.

Westbury to Bath should be a near normal timetable, while Westbury to London Paddington should not be affected to any great extent either. The Hearts of Wessex line connecting Bristol via Trowbridge and Westbury to Weymouth will also continue during this period but with some inevitable disruption.

During stage two, from August 1-31, the Avon Valley line connecting Westbury to Bath will be closed entirely, with replacement buses operating to the stations from Westbury to Bath along that line.

Westbury to Cardiff trains after Trowbridge will be diverted to Swindon, with alternate trains calling at Melksham. The Bristol to Waterloo service will not run during August, but may start from Westbury.