South Western Railway (SWR) has announced a temporary reduction to its summer timetable, with minor alterations to suburban services to support a critical phase of driver training for its long-awaited fleet of new Arterio trains.

The reduced timetable will run until 29 August, with the operator confirming that fewer than 5% of its 1,600 daily services will be affected.

However, specific timetable changes have not yet been made publicly available.

SWR, which became the first train operator to be re-nationalised under the new Labour government in May, said the summer changes coincide with a seasonal fall in passenger numbers.

A spokesperson for SWR said:"Over the summer holiday period, customer numbers drop by 12–17%, and the services we have removed are those with the lowest forecast demand."

The company added that the summer timetable changes will also help minimise the risk of unexpected cancellations due to staff taking annual leave over the school holidays.

The decision comes as SWR steps up training for its drivers to operate the Arterio trains, a long-delayed modern fleet now beginning to enter service.

So far, 14 Arterios are being used in daily operations following the transfer to public ownership.

The affected routes where amended timetables will be in place include:

• Alton
• Chessington South
• Guildford via Cobham & Stoke D'Abernon
• Guildford via Woking
• Hampton Court
• London Waterloo via Richmond
• Reading
• Shepperton
• Weybridge via Chertsey
• Windsor & Eton Riverside
• Woking (stopping services)

Reacting to move, Richmond Council Chair of the Transport and Air Quality Services Committee, Councillor Alexander Ehmann, tweeted: "Yet again, a weakening in services.

"No engagement, no consultation. South Western Railway need to show up and explain the detail of these changes."

Customers are advised to check train times before travelling, especially if using services on the affected routes.

For up-to-date travel information and to view the summer timetable, visit the SWR website.