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The M23 was closed both ways near Gatwick, with landslips shutting train lines.
- Copyright: Southern
Heavy rainfall is continuing to cause major disruption across the Southern, Thameslink and Gatwick Express rail network.
Disruption is expected to continue until the end of the day.
Two areas have been worst affected:
- Three Bridges to Brighton (flooding at Balcombe) -there is no direct service from London to Brighton, Lewes or Littlehampton.
- Warnham and Ockley cannot be served due to local flooding.
On Southeastern a landslip between Robertsbridge and Etchingham means trains are currently unable to run between these stations. Disruption is expected until 19:00.
There has also been a landslip between Strood and Maidstone West, blocking the lines there too. Disruption is expected for the rest of the day.
- Copyright: Eddie Mitchell
The M23 motorway in West Sussex is now open again in both directions following earlier flooding, Sussex Police said.
- Copyright: BBC
Here are some pictures of flooding in Lamberhurst, Kent.Copyright: BBC
Highways officials in West Sussex say they are "alarmed" by reports of motorists ignoring road closure signs following the widespread flooding.
People coming to Medway from London later will be able to use the St Pancras to Maidstone West services if they need to get to Rochester, Chatham or Gillingham.
Aerial video shows floods in South East England, including the M23 which is closed.
- Copyright: BBC
The bank of the River Tiese has burst at Lamberhurst, Kent.
The river water has now flooded people's gardens.
BBC Live reporterCopyright: Ellis Hart
Ellis Hart was on his way to a work Christmas meal, but missed it when he got stuck in the M23 backlog following severe flooding.
The stone restorer was stuck near to Pease Potage for more than two hours, after the motorway flooded.
Mr Hart, 26, said: "We were all going for a curry in London, paid for by the boss. It was our Christmas bonus.
"I was looking forward to that, but I've missed it now.
"I was meant to get the train, but saw the 10:04 was cancelled so jumped in the car to drive.
"I didn't check the traffic online, but there were no police, or signs anywhere to say the road was closed, or diverting people.
"I'm just glad I didn't bring my three kids with me. I was going to drop them off with my mum on the way."
Six hours ago Sussex Roads Police tweeted: "We are trying our best to get you turned around, but please be patient: with the road closure on, there's a lot of traffic to move into a very small space at Pease Pottage."
- Copyright: Network Rail
Rail operator Southeastern says a landslip at Robertsbridge means no trains are running between Tunbridge Wells and Hastings.
Both lines have been blocked. Trains have been cancelled, delayed or revised. And the disruption is expected to continue until 19:00.
Network Rail response staff are on site.
BBC Live reporter
Many rivers in Kent are now close to overflowing.
Glenn Ebrey is in Edenbridge.
With flood water high in places, West Sussex Fire and Rescue Service have urged motorists not to drive through flood water.
Meanwhile, in neighbouring East Sussex, fire officials there have asked people to only call 999 in an emergency.
- Copyright: Eddie MItchell
Highways England say there is no estimated opened time for reopening the M23, which is flooded across both carriageways between junctions 10 and 11.
However, the stream of water onto the road has been stemmed and they are "making progress", a spokesperson said.
A fresh landslip is causing new problems on the rail network in parts of East Sussex this afternoon.
Trains are not expected to start running again until 15:00 GMT.
Heavy rain caused a high water level at Frant, East Sussex, earlier which affected the signalling system.
It has now been sorted out, but there are still knock-on delays from issues in other areas.
The M23 is closed between junctions 10 and 11 in both directions in West Sussex, Highways England said. Footage from Eddie Mitchell shows Highways England teams out in force on the motorway.
Services between Brighton and Gatwick have been vastly cut back as a result of the weather.
- Copyright: Thameslink Railway
If you're travelling on the following routes your journey will be delayed by about two hours due to flooding on the tracks, Thameslink Railway has warned:
- Between Brighton and Gatwick Airport:
- To and from Uckfield
- Warnham & Ockley
- Mitcham Junction / Eastfields
People are advised to check before they travel.