Merseyrail Hunts Cross line closure: Why tunnels need repairs

Helen Little, from Network Rail, said: “These tunnels are over 100 years old, so over time they will naturally deteriorate.”

She said there were numerous wet patches inside the tunnel and the waterproofing would divert water down the side walls, rather than allowing it to fall on to the tracks.

Merseyrail trains are powered by an electrified third rail running alongside the tracks, and Network Rail said water reaching it could trigger faults and power failures.

“Keeping the water from the rail stops the deterioration of the third rail and also stops faults,” Little said.

She said losing power through the rail could prevent trains from running.

The waterproofing work forms part of wider improvements to four Victorian-built tunnels serving the Northern Line.