Commuters have been warned not to travel on Tuesday morning after severe flooding prompted transport chaos, with dozens of trains cancelled and roads left gridlocked.
Police also shut a section of the M25 overnight after discovering two sinkholes on the central reservation. The motorway was closed in both directions but Highways England said the sink holes had been repaired and the road reopened by around 6am.
But motorists faced further delays after the M25 was closed in both directions between junctions three and four due to an incident, Kent Police said.
Weather warnings remain in place for much of the day, with forecasters predicting parts of the UK could be inundated with more than 100mm of rain this week.
At Brookwood station in Surrey, passengers said they were forced to wade through almost eight inches of water after the underpass flooded.
One commuter shared a picture of a man who had rolled his trousers up in order to reach the platforms.
Trains through Orpington were suspended after several inches of rain fell onto the tracks, while a tree blocked lines between Wokingham and Reading.
No trains were stopping at Mitcham Eastfields, Mitcham Junction, Hackbridge and Carshalton after all Wimbledon Loop services were cancelled.
Services between London Bridge and Sutton, London Victoria to Sutton via Norbury, London Victoria to Epsom and Milton Keynes Central and Clapham Junction were also suspended.
Southern, Great Northern and Thameslink services are expected to be disrupted all day, with the operator advising passengers to “avoid travelling if possible”.
On the National Rail website, it said: “If you intend to travel, you may wish to delay your journey, or use alternative routes. Your journey times will be heavily extended.”
Disruption was also expected on services into London Waterloo after an “operational incident,” with services delayed by up to 15 minutes until 10am.
One commuter said: “I have been stranded on a London Bridge to Orpington train for the past 50 minutes. This is because of severe flooding in the Orpington area which is covering the rails.
“The driver is now walking to the other end of the train and will drive it back in the opposite direction to Chislehurst where we’re all going to get off there instead.
“My car is parked at Orpington, terrific. Apparently there are other trains ahead and behind us in the same situation.”
North-eastern parts of England and the Midlands are expected to bear the brunt of the downpours on Tuesday, with a yellow warning in place until midnight.
Some areas set to see up to 60mm of rain, particularly over the first half of the day, according to the Met Office.
Another warning covers Devon and Somerset, where similar conditions are expected.
The Environment Agency has issued three flood warnings in south-east England, for the River Wandle at Morden, south London, the Emm Brook at Wokingham and Ravensbourne at Bromley.
The agency said on its website: “River levels have risen as a result of localised thunderstorms. Flooding of property is expected imminently. Please take action.”
A total of 31 flood alerts – which mean flooding is possible – are in place across the country.
On Wednesday and Thursday, some parts of the UK could be struck by 60mm to 80mm of rain, and possibly even up to 100mm.
Met Office meteorologist Alex Burkill described the figures as the “worst-case scenarios” but added that people need “to be aware that we’re in for some treacherous weather”.
“If you add it all up some places are likely to see over 100mm this week, which is around double the average they would get in the whole of June,” he said.
Residents are being told to avoid low-lying footpaths near local watercourses and plan driving routes to avoid low-lying roads near rivers which may be flooded.