A complex track renewal through a narrow Victorian tunnel has been completed to enhance journeys for passengers and freight on the UK’s West Coast Main Line.

Network Rail and its contractors carried out the upgrade on one of Europe's busiest mixed-use rail routes.

The focus of the work was on the Northchurch Tunnel between Berkhamsted and Tring.

The renewal work, which began on New Year's Eve, involved replacing 400m of railway line.

The Central Rail Systems Alliance, a partnership of Network Rail, Balfour Beatty, Atkins, and TSO, delivered the project.

The upgraded section includes three tunnels where the faster lines share one tunnel, and the slower lines have individual tunnels, the oldest dating back to 1836.

Six engineering trains were utilised, and staff worked a total of 2,440 hours to complete the job. Due to the project's complexity, the slow lines were closed, with all trains using the fast lines during the project.

The lines reopened on Saturday (4 January).

This project was completed in the railway's 200th anniversary year, marking the bicentenary of the first passenger railway between Darlington and Stockton in September 1825.

Network Rail Capital Delivery senior programme manager Neil O’Toole said: “We know there’s never an ideal time to close a section of railway, so I’d like to thank passengers whose journeys may have taken a little longer while we made these important improvements through Northchurch Tunnel.

“This track renewal was a bit of a Rubik’s Cube to complete as we had to do each stage in a predefined sequence and the job took nearly three years to plan. It was our priority to make it work and get the railway reopened on time. From today passengers will have a much smoother ride and fewer delays caused by further maintenance now we’ve brought the track here bang up to date.”

In November last year, Network Rail Property announced plans for redeveloping London Liverpool Street Station to enhance the customer experience.