A tunnel that was built by the Victorians in 1878 will form a crucial part of the impressive Crossrail network in London.

Some 13 million litres of water have been drained from the Royal Victoria Dock to allow Crossrail to access the Connaught Tunnel from above and the organisation will now perform the engineering equivalent of open heart surgery on the passageway.

The tunnel has been out of action since 2006 and some parts are in a poor state, so major work is required to ensure it is safe enough to accommodate Crossrail trains from 2018. It is the only existing tunnel that will be reused in the project.

Overall, the Crossrail development will see 21 km of new twin-bore tunnels being constructed and the team tasked with delivering the ambitious transport network first started digging last year.

Linda Miller, Connaught Tunnel project manager, said:"The Connaught Tunnel is testament to the engineering skill of the Victorians, but after 135 years there's a lot of work that needs to be done to get it ready for Crossrail."

Once the south-east section of Crossrail is open, up to 12 trains per hour will run in each direction through the Connaught Tunnel.