Passengers are being urged to avoid one of the UK’s busiest rail routes next week during emergency work to repair a landslip.

Network Rail said South Western Railway services between Woking, Surrey and Basingstoke, Hampshire will be disrupted.

Routes to Bournemouth, Dorset; Salisbury, Wiltshire; and Southampton, Hampshire, will be affected.

The work is being timed to coincide with industrial action by train drivers’ union Aslef, which was already due to cause cancellations.

Tiny sensors in the ground detected movement in a 100-metre-long slope next to St John’s Hill Road bridge between Brookwood and Woking.

Cracks up to 45 metres long, 50cm wide and a metre deep were discovered.

Network Rail has imposed a 20mph speed limit on trains passing through the area before the work begins.

The Government-owned company said it will close part of the railway to stabilise the cutting and prevent a more disruptive and potentially dangerous landslip, which is “highly likely if action isn’t taken” due to a forecast of cold and wet weather.

Specialist equipment and machinery will be brought onto the site this weekend, before work to build a metal wall starts on Monday December 4.

Some 170 pieces of steel each 10 metres long will then be driven into the ground at the base of the slope from Wednesday December 6 to Sunday December 10, except on Thursday December 7 when passenger numbers are expected to be high following disruption due to strike action the previous day.

Two of the four tracks on this stretch of railway will be closed while the work is taking place.

Trains will also need to be manually signalled by engineers using red and green hand signals, further reducing the number of services that can run.

Only three trains per hour will be able to run in each direction, down from 16 normally.

Network Rail Wessex route director Matt Pocock said: “I would like to thank customers and local residents for their patience and understanding over the coming week while our teams work tirelessly to complete emergency work to stabilise this precarious cutting between Woking and Brookwood.

“There is never a good time to close any part of the railway but the safety of our customers and railway colleagues is our number one priority.

“It’s imperative that we act now to prevent any further landslip, which would cause even longer delays.

“We have worked closely with our colleagues at SWR to identify the least disruptive time to do this and next week provides an opportunity with industrial action reducing the number of services that will be in operation. However, unfortunately there will be severely reduced services as a result.”

South Western Railway chief operating officer Stuart Meek said: “We’ve worked closely with our colleagues at Network Rail to ensure that landslip repairs are carried out as quickly as possible while causing the least amount of disruption to our customers.”

Passengers are being urged to “only travel if their journeys are absolutely necessary” during the work.

They are advised to check online journey planners.

Network Rail has said it will have less money for maintenance over the next five years due to budget constraints.