Only one in four Thameslink trains will run during the rush hour this evening (Friday 23 January) after flooding in a tunnel between Farringdon and St Pancras in London.
Thousands of passengers returning to Brighton are likely to be affected by delays and cancellations while Network Rail pumps out the water. A 16in water main burst.
Thameslink said: “Some trains are continuing to run safely through the tunnel as Network Rail pumps water in a bid to maintain it at a steady depth.
“But there are major delays and the service has had to be significantly thinned out.
“It is understood that water company engineers need to isolate the leak without cutting off essential supplies to a nearby hospital.
“Even if leak is repaired soon, there will be a major knock-on impact on this evening’s services.”
Thameslink’s passenger service director Stuart Cheshire said: “We’ll do our very best to get people home tonight as quickly as possible but the burst water main is causing significant disruption.
“We’ve brought in buses and extra staff and we’re pushing out messages through all available means to encourage people to start home earlier if possible and to leave longer for their journeys.
“Passengers can claim compensation for the delays via our website thameslinkrailway.com/delayrepay.”
Thameslink services are already hit by the continuing work to modernise London Bridge Station.
Passengers heading to or from Luton Airport also face delays over the weekend.
The company said that they should allow an extra hour to cross London from 11.45pm tonight until the early hours of Monday (2 February).
It said: “Essential improvement work being carried out by Network Rail to improve the track and overhead lines between St Pancras and Kentish Town means there will be no Thameslink or East Midlands trains between West Hampstead Thameslink station and Farringdon in central London.”