Image source, PA Media

A quick recap:

• Two passengers suffered serious injuries and 18 others were less seriously injured in Thursday's derailment, which happened with 150 people on board.
• A community hub opened after the incident, with locals helping passengers as they left the scene.
• British Transport Police says the two seriously injured people are not thought to have life-threatening injuries.
• Network Rail said there were no significant injuries after a second derailment near Wickford in Essex on Friday.
• Rail Accident Investigation Branch inspectors remain at the Lewes gathering evidence.
• Preparations are under way to remove the derailed carriages.
• The line between Haywards Heath and Lewes remains closed.

• Greater Thameslink Railway says the railway remains safe and described accidents of this nature as rare.
• The role of the hot weather has not been established and remains under investigation.

Image source, Eddie Mitchell

Image source, Eddie Mitchell

Sussex Police and Crime Commissioner Katy Bourne says the region is supporting the emergency workers and those who were on board the train.

“Sussex has always shown remarkable resilience during emergencies and I know the community will continue to support one another in the days ahead," she says.

After a "deeply unsettling" incident, she urges those involved to seek emotional or practical support from commissioned victims' service providers.

Network Rail has just released a statement.

It says investigations into two train derailments in two days “will look at all possible causes and factors”.

Safety director Martin Frobisher says the hot weather has “presented exceptional challenges to the railway”.

Steps being taken include temperature monitoring, speed restrictions where appropriate, and planning track renewals around high temperatures.

Frobisher adds the focus is "to get services back running safely as quickly as possible".

More now on the safety of the railway.

To recap, there have been two derailments within 24 hours - one in East Sussex, another in Essex.

Richard Bowker, former chair of the Strategic Rail Authority, says there are “very strict, very effective processes and protocols” for when there are high temperatures on the railway.

"We have one of the safest railways in the world. That did not change yesterday,” he adds.

“But what we do need to now understand is exactly what happened here.”

Bowker says incidents like this are “extremely rare”.

He says investigators will look at the condition of the track, the effects of the heat, the train itself, and the embankment.

Image source, Jack Valpy/BBC

We've spoken to Sim Harris, the managing editor of Rail News.

He says The Rail Accident Investigation Branch usually tries its best to produce an interim report "within days" of serious incidents.

More of the track between London and Eastbourne has been closed following an inspection.

Southern Rail says: "A safety inspection of the track has taken place between Polegate and Eastbourne - and all lines have been blocked.

"No trains can run between these stations in any direction until further notice and you will need an alternative route."

The line between Haywards Heath and Lewes is already closed after the derailment.

Eastbourne is expecting thousands of visitors this weekend as it hosts the popular Airbourne air show.

Stay with us for more updates.

Two derailments have happened within 24 hours - one in East Sussex and another in Essex.

Former transport minister and ex-Lewes MP Norman Baker says there's no need for people to panic over safety on the railway.

“I suspect there may be a climate-related incident here, either in terms of the ground beneath the rails giving way or alternatively the rails buckling during extreme heat,” he says.

"Stick to the railways," he says.

“I was on the train today between Lewes and Seaford and perfectly happy to do so.”

Yana Ludwig, 56, from the United States, was on the train and tells the BBC the experience was "completely terrifying", with "banging" before "everything went topsy-turvy".

"It seemed like a really long time but it probably was 10 seconds of that before the carriage actually fell on the side," she says.

She says everyone on the train was checking on their fellow passengers.

"These moments everybody kind of pulls together," she says.

James Abbott, the consultant editor at Modern Railways, says: "We don't want to speculate and it is early days, but I would not be surprised if the weather and climate change were to be a factor.

"Climate change is a difficult problem for the railways.

"Earthworks and cuttings are full of water in winter then short of water in summer," he says.

"It could be the ground underneath the railway has dried out and caused it to collapse."

A Greater Anglia train has derailed near Wickford in Essex, the BBC understands.

It's the second instance where a train has come off the tracks in two days, after Thursday's incident near Lewes.

You can find more on this breaking news story on our colleagues' live page.

Image source, Getty Images

Trains between London Victoria and Eastbourne this weekend are cancelled, Southern Rail says.

The seaside town is expected to get a bumper number of visitors this weekend as it hosts the Airbourne air show.

To travel between Victoria and Eastbourne, passengers are being advised to go via Brighton.

Southern says Cooksbridge and Plumpton will also not be served all weekend, with rail replacement buses operating between Lewes and Haywards Heath.

Check for updates on your journey on Sunday evening if you're planning to travel on Monday, it advises.

Image source, PA Media

Oriana Evans, 54, who lives in the area, says she is "really proud of my community" for helping the passengers on the derailed train.

The nearby Landport Community Hub took in people from the train while other residents offered lifts home and water.

"It could have been totally different," she says.

"I think they were really lucky with where it's happened with the train slowing down, and access through the fields with the farmer's gates there, and the fact it was in Landport and the community hub was really nearby"

Katy Austin
Transport correspondent

The simplest answer is because the exact cause is not yet known.

Speculation tends to emerge as people look for quick answers.

But it’s for specialist accident investigators to come up with answers, and they won’t be instant.

As journalists, at this point, we can put questions to the organisations involved, but answers do not necessarily come, partly because they don’t want to get in the way of accident investigators’ work.

Photos of the track are not conclusive because we don’t know what it looked like before the back three carriages derailed.

For example, a tweet from Southern rail suggests there was a safety inspection of the track between Lewes and Haywards Heath on Wednesday.

Network Rail has not yet confirmed this, what any findings were, and not if action was taken in response.

It’s also not said whether any speed restrictions were in place in the area.

So while there’s no doubt this was a serious incident, plenty of questions remain unanswered.

Image source, George Carden/BBC

Wendy Baker, a trustee of Landport Community Hub, says she "would be very shocked if anyone on the estate hasn't felt affected" by the incident.

The hub opened up to take in passengers from the train and to offer help including lifts home, chargers and water.

"Within minutes we were open and we had chairs out and we had community people just naturally coming down to us providing water and snacks and just offering anything that needed to be done," she says.

The trustee, who lives in the area where the train derailed, says the mood in the hub was "bizarre" following the derailment, but that "everyone was very calm, very humble, very grateful".

More now from the British Transport Police, who have also praised locals in the area for their role.

A spokesperson says: "The local community came out to assist emergency services and provide support and refreshments to passengers that were on board the train.

"Lamport Community Hub was opened as a place of safety to facilitate medical treatment and offer relief from the hot weather."

The force is now asking for anyone who was on the train and has not spoken to them yet to come forward.

BTP Assistant Chief Constable Ian Drummond-Smith said: "Our thoughts remain firmly with those who were injured and their loved ones.

"The public can expect to see a continued police presence at the scene over the coming days as the Rail Accident Investigation Branch's investigation to identify the cause of the derailment continues.”

Two people who sustained serious injuries in the derailment are not deemed to be in a life-threatening condition, British Transport Police has confirmed.

Jon Leach, from the RMT, says the union is "stunned and shocked and very, very concerned that this could even happen".

"We must learn from this, and we must learn the lesson that you cannot operate a railway without professional railway staff," he says.

Leach also praises the on board supervisor who gave an announcement to passengers after the train derailed.

"What an utter professional, We should all be very proud of him, and we are too," he says.

"What I will say is he is putting his absolute primary responsibility first, which is the safety of them passengers on the train as well as his colleagues.”

Rachel Heath, from London, and Tracy McGregor, from Eastbourne, have shared what was going through their minds as the train they were on derailed.

To listen to more, visit BBC Radio Sussex.

Image source, Rob Bradley

Deputy leader of Lewes District Council Christine Robinson says the response to the incident "puts your faith back in human nature".

"Obviously people in Lewes always rally around things like this anyway, and it's community at its best, isn't it? When they respond and react to things like this," she adds.

Robinson also praised the response from passengers who were on the train during the "harrowing" experience.

"Psychologically it's going to take some of these passengers a long, long time to recover from this," she says.

Katy Austin
Transport correspondent

The Rail Accident Investigations Branch (RAIB) says it will provide a further update "next week once we know more".

A spokesperson confirms its inspectors are on the scene and will continue to gather evidence at the site of yesterday's derailment at Lewes.

The evidence includes examining the accident site, including the derailed train, and railway infrastructure.

They’re collecting and reviewing evidence such as CCTV footage, signalling data, and data downloaded from the train.

They added the RAIB "will conduct a full, independent safety investigation into the accident."