A £10m programme of repair work to the Blackheath tunnel by Network Rail is to take place this summer.

Passengers in south-east London have been asked to plan ahead from Sunday 18 May to Sunday 27 July 2025 as the Blackheath tunnel, between Blackheath and Charlton will close as Network Rail begins essential repairs to the 175-year-old Victorian-era structure.

The work follows a 10-week closure last summer, during which engineers 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.

Services that normally run through the tunnel will be diverted via other routes during the 10 weeks.

The work is needed because the one-mile-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.

While the tunnel is safe, the leaks and very wet conditions inside it damage track and electrical equipment, causing delays and speed restrictions.

Over the last year, faults in the tunnel have been the cause of around 1,000 minutes of delay to Southeastern passengers.

David Davidson, Network Rail’s Kent route director, said: “We know there’s never a good time to close the railway, and that changes to services for a 10-week period is a long time.

“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.

“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.

“When the tunnel is repaired with water damaged infrastructure replaced and the tunnel waterproofed, passengers will benefit from fewer delays, fewer speed restrictions and improved reliability.”

Over the course of 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’ – in other words, dealing with waterlogged sections of track that cause bumpy train rides for customers. The additional work means less disruption for passengers in the long term.

When the tunnel is repaired and water damaged infrastructure replaced passengers will benefit from fewer delays, fewer speed restrictions and improved reliability.

Around 3,500 passengers per week usually travel to stations between Lewisham and Abbey Wood through the Blackheath tunnel.

To minimise disruption and keep passengers moving when work is taking place, services from Dartford to Cannon Street (via Charlton and Lewisham) will run instead via Greenwich, stopping additionally at Westcombe Park, Maze Hill, Greenwich, and Deptford. This offers the option to travel on the DLR from Greenwich to Lewisham, adding around seven minutes to journeys.

Other services will be diverted along the Bexleyheath line.

There will be no rail replacement buses but passengers will be able to travel on selected Transport for London bus routes at no extra cost.

A taxi can be provided for customers with accessible needs for travel between Blackheath and Charlton.