The Severn Tunnel will be closed for six weeks from mid-September to upgrade it in preparation for a fleet of new electric trains offering more seats and faster journeys.

The closure of the four mile long, 130-year-old tunnel will affect the majority of passengers who travel into and out of South Wales including those to and from London, Portsmouth Harbour and south-west England.

Passengers travelling to and from London Paddington will be diverted via Gloucester with extended journey times of up to 35 minutes and a reduced frequency of trains. Rail replacement buses will be in operation for all other services.

Ahead of the upgrade, a significant amount of preparation work is being undertaken, with four tonnes of soot being removed from the tunnel as well as repairs to the brick work.

During the closure, Network Rail’s orange army will be working all day and night to install over eight miles of conductor rail to power the new trains.

Paul McMahon, route managing director for Network Rail Wales said that without a solid six-week closure it would take engineers up to five years to complete the work.

“While the project will result in short-term disruption, there are significant long-term benefits, including faster, more frequent trains and a boost to economic growth in towns and cities across South Wales thanks to improved connections to and from London,” he said.

Rob Mullen, Great Western Railway General Manager Central added, “The electrification of the line will enable us to deliver more frequent services, more seats, and to reduce journey times into London by as much as 20 minutes from Swansea. Electrification will also deliver a greener and quieter railway, resulting in cleaner air and a reduction in the noise for those living near the railway.”