Failures uncovered after the partial collapse of a railway tunnel could have led to “severe consequences” for passengers, a damning report has found.

Chaoswas caused on the rail network when Balcombe Tunnel was shut for nearly 24 hours in 2011.

An emergency inspection called after engineers noticed a sagging beam revealed 18 studs missing and five loose.

The sagging beam would have posed a “significant risk” to regularly passing trains had it dipped further.

The findings follow an investigation by the Rail Accident Investigation Branch (RAIB) launched after chaos crippled the Sussex network on September 23, 2011.

 

MORE:

 

Thousands of commuters faced long delays after services between HaywardsHeathandThree Bridges were cancelled. The disruption led to transport minister Norman Baker calling for the reopening of the old Lewes to Uckfield line.

The RAIB investigation revealed 18-inch studs which held the tunnel beans in place had been reported missing as early as 2008.

But Network Rail failed to support an engineer with “limited inexperience” and the missing studs were not properly reported.

RAIB said the engineer had not appreciated the risk and did not consider the problem might require investigation.

Meanwhile inadequate technical data led to the insufficient resin being used in damp conditions.

Poor access to the busy tunnel meant examinations were not to usual standards.

Tim Robinson, Network Rail’s routemanaging director for Sussex, said: “We are reviewing the Rail Accident Investigation Branch’s recommendationsandhave already implemented many of them.

“We have reviewed our inspection regime and the materials used within the tunnel to minimise the risk of future incidents and identify potential faults for repair before they pose a risk.

“Much of the network’s infrastructure dates back to the Victorian era and its maintenance has been undertaken in different ways by different organisations.

“A priority for Network Rail is to continue to upgrade all our assets and bring our entire infrastructure into line with our modern maintenance practices.”