- Downpours across the South East late last night and into this morning have left roads impassible
- Commuters travelling into the capital were hit with cancellations of train services and delays on roads
- The rain is now moving west, with Gloucestershire and South Wales facing a soaking this morning
- Police are urging drivers to reduce their speed on the M4 after a jackknifed lorry caused long tailbacks
Published: 07:34 GMT, 11 May 2016 | Updated: 10:05 GMT, 11 May 2016
The Royal Windsor Horse show was cancelled today after torrential rain fell across the South East overnight, flooding some areas and causing chaos on roads.
The event - which was due to host one of the main celebrations for the Queen's Birthday - had to be called off after the deluge left much of its car park under water.
Nearly no area in the South East escaped a soaking as parts of the Home Counties saw half a month's worth of rain fall in just 12 hours.
Parts of London have been shut down by flooding this morning and the Met Office has issued a yellow warning of up to 25mm rain for the whole of the south coast.
A statement on the Royal Windsor Horse Show's website stated: 'Organisers have announced that today's show is cancelled due to flooding in the public car park and lorry parks. The rain is expected to leave by lunchtime and tomorrow's events are planned to go ahead as usual.'
The Royal Windsor Horse Show, which was due to host one a celebration for the Queen's birthday, was cancelled today due to flooding
Disappointing fans trudge through water at the entrance of the hose show, whose organisers were hoping for a special day for the Queen today
Fans put on a brave face as organisers said heavy rain had left the car park under water, leaving equine sports lovers unable to attend
Some of the beautiful horses taken to the show in Berkshire were taken to exercise in the mud by their owners this morning
South Farnborough in Hampshire saw the worst of the weather - with 27mm of rain falling between 6pm last night and 6pm this morning. The area usually only sees an average of 54mm of rain in the entire month.
Heavy rain closed the A20 in Lewisham in the south-east of London as a section of the road was left under at least a foot of water. The district's station was also inaccessible.
Photos of the scene show a motorist stranded in his car as the flood rises around him and rescue workers work to pump away the deep water.
Transport for London warned drivers: 'Road is now impassable both ways by Lewisham roundabout. Not worth trying to drive through, don't be that guy!'
The heavy rain also brought trains into London to a standstill, with DLR services cancelled between Deptford Bridge and Lewisham.
Kew Gardens experiencing the wettest six-hour period, clocking nearly an inch of rain. Charlwood closely followed, with just under an inch falling on the Surrey village and more than 18mm of rain recorded in just one hour at St Catherine's Point on the Isle of Wight.
Steven Keates, from the Met Office, said across southern, central and western Britain it has been a 'pretty soaking night' with some 'intense downpours'.
'It is atrocious out there - driving will not be that pleasant on some roads across the South this morning,' he said.
The rain is expected to move west today, battering Gloucestershire, Somerset and South Wales, but should clear by the end of the week
This was the scene in Lewisham, south-east London early this morning after torrential rain left the road next to the area's train station flooded
The flooding caused the usually-busy A20 main road to be shut and train services between Lewisham and Deptford to be cancelled
A fireman surveys the scene beneath Lewisham railway bridge after heavy rain flooded the road and caused train services to be cancelled
Commuters in London (left) and Bristol (right) had to walk to work in the rain as the wet conditions moved westwards during the morning
In Berkshire, there were long delays on the M4 after a jackknifed lorry blocked one carriageway and caused miles of tailbacks on the other. The AA tweeted: 'Accident on M4 - avoid Reading area.'
Police in nearby Newbury warned of dangerous conditions and slammed 'lunatic' drivers after a spate of aquaplane smashes on local roads.
A traffic officer said: 'Many drives are tearing along at upwards of 80mph when they can't see a thing because of the spray thrown up by other vehicles. Apart from being blinded by the sheets of spray, they are also likely to aquaplane on the pools of rainwater which are forming on the road surface.
'Their wheels will lose grip with the road and they will go into a spin - it's crazy the way some of them are tearing along, completely ignoring the conditions.'
The rain is expected to clear in the South East today and move west, with Gloucestershire and Somerset expected to see the heaviest showers this morning and this afternoon.
A jackknifed lorry was causing major disruption to rush hour traffic on the M4 motorway near Reading, Berkshire this morning
A picture taken by a stranded motorist shows emergency services dealing with the crash, which closed the busy motorway this morning
A traffic map tweeted by the AA shows the resulting disruption caused to the roads around Reading as police dealt with the crash
Forecaster Mr Keates added: 'This wet weather will gradually work its way south and west over the course of this morning and into the afternoon.
'The likes of Devon, Cornwall and South Wales will see some heavy rain over the next few hours, with an improving picture across London and the South East.
'But there is scope for some heavy thundery showers around this afternoon. There will be some sunshine around and temperatures will be in the high teens giving it a humid feel.'
Mr Keates said the weather in the South is in 'stark contrast' to warm and sunny weather over western Scotland and northern England.
Looking ahead to the rest of the week he said there is an 'improving picture' across the country and the potential for some showers in the south-west of England.
Temperatures could reach the low 20s on Thursday with these dropping by the weekend to the seasonal average of the mid to low teens.
Horse riders in the sea mist at Keyhaven Marshes, Hampshire as wet weather and flooding affect the whole of the south of England
Met Office maps from 3am last night show up to 16mm of rain falling an hour in parts of London with a band of rain across the Home Counties
A rain map from this morning shows the wet weather has now moved west, with Gloucestershire coming in for some of the heaviest showers
The Met Office has issued a yellow warning for rain across the entire south coast and parts of South Wales for today