One of Britain’s busiest railway lines will be closed for nine days from Saturday, causing major disruption to passengers.

No trains will operate on the southern end of the Brighton Main Line (BML) until February 25 to enable Network Rail to carry out work as part of a £67 million upgrade.

The BML is normally used by 300,000 people each day and connects the south coast with London on Southern and Thameslink trains.

The Three Bridges-Brighton and Three Bridges-Lewes services will be affected by the closure.

Network Rail warned that journeys will be “significantly longer” and trains will be “much busier than usual”.

Some of Britain's busiest rail routes will be closed (Network Rail/PA)Some of Britain’s busiest rail routes will be closed (Network Rail/PA)

Services to and from Brighton will be diverted along the coast via Littlehampton, adding an hour to journeys.

A replacement bus and coach service will be in operation, featuring more than 240 vehicles every day.

Derby County supporters will be among those disrupted when they travel to watch their team’s FA Cup fifth round match against Brighton and Hove Albion on Saturday.

Research by watchdog Transport Focus indicated that 52% of passengers support the work and 47% are satisfied with the information provided.

More than three out of four (76%) will take action such as work from home, take annual leave or avoid peak travel times.

Network Rail claimed reliability on the BML would deteriorate if it did not carry out the work.

The closure is timed to coincide with half term as fewer passengers use the railway during school holidays.

John Halsall, Network Rail’s managing director for the South East route, said: “This work is absolutely critical as this stretch is one of the most unreliable parts of the network, accounting for half the delays to trains arriving from the South into central London.

“We know it’s never a good time to close the railway, but the only alternative would have been to close the line for 84 weekends over the course of two years.

“Doing the work over this nine-day period means we can achieve so much more and deliver the punctuality and reliability benefits to passengers much sooner, plus the railway is much quieter during the school holidays.

“Working with our colleagues at Govia Thameslink Railway, we are making every effort to enable those passengers who need to travel during this period to do so comfortably.”

Network Rail will renew and upgrade track junctions and signalling, shore up embankments and install technology to detect potential problems before they occur and help the services recover faster when there is a fault.

Extensive work will also be carried out within four Victorian tunnels to stop leaks and drainage issues which cause major delays.

The BML will also be closed during several additional weekends until May.