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 £67m upgrade.

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

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.”

Halsall said the route will be working with Govia Thameslink Railway, “making every effort to enable those passengers who need to travel during this period to do so comfortably”.

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

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

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, with more than 240 vehicles transporting passengers 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-in-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.

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.

Rail fares increased by 3.1% on average this year despite punctuality falling to a 13-year low after a number of major issues disrupted Britain’s railway service in 2018.

Some 14% of trains were late last year, with several franchises recording even worse performances.