Network Rail’s Blackheath Tunnel in south-east London is to close for 10 weeks for the second phase of a £10m repair programme.

The work follows a 10-week closure last summer, during which VolkerFitzpatrick Southern Renewals Enterprise cleaned soot from the tunnel lining, carried out detailed surveys and replaced thousands of bricks to stop water leaking into the tunnel and damaging the railway.

The work is needed because the 1.6km-long tunnel, which opened in 1849, is prone to leaks and water damage. The tunnel’s brickwork is affected by the freezing and thawing of rainwater which filters through the ground into the tunnel. Network Rail says the tunnel is safe, but the leaks and wet conditions damage track and electrical equipment, causing delays and speed restrictions.

Over the past year, faults in the tunnel have caused around 1,000 minutes of delay to rail services.

Network Rail’s Kent route director, David Davidson, said closing the tunnel for a 10-week period was the most efficient approach.

“We are carrying out the repairs over a series of 10-week closures because working in cramped and narrow tunnels is incredibly difficult. If traditional weekend working was used, engineers would spend at least 50% of a weekend bringing materials and plant in and out of the tunnel, leaving limited time for actual work,” he said.

“We are sorry for the inconvenience caused by the closure, but this is a long-term project and this will be the last closure until we are back in to finish over summer 2027.”

Davidson said once the tunnel was repaired, with water damaged infrastructure replaced and the tunnel waterproofed, passengers would benefit from fewer delays, fewer speed restrictions and improved reliability.”

Over the entire programme of works, Network Rail will replace thousands of bricks and install a new tunnel lining to stop water leaking into the tunnel.

Drainage systems will be rebuilt and essential track work carried out, including the removal of ‘wet beds’ – waterlogged sections of track that cause bumpy train rides.

The works will be carried out from May 18 to July 27 and rail services will be diverted to other lines.

Around 3,500 passengers travel through the Blackheath Tunnel each week.