Wreaths will be laid and a minute’s silence held to remember the 35 people killed in a train crash in south London 30 years ago.
At 08:13 on 12 December 1988 faulty wiring and signalling caused three trains to collide in Clapham.
Survivors and families will pay their respects to the dead and almost 500 injured people at a church service.
Bosses from the emergency services and rail industry representatives will also attend memorial events.
A 250-page report on the findings of the accident inquiry, chaired by Anthony Hidden QC, found faulty wiring had caused an incorrect signal to be displayed to a train driver, who was driving into a blind bend and had no chance of stopping.
His train, which had come from Poole, ploughed head-on into the back of a stationary train, from Basingstoke.
The Poole train then veered and hit an empty oncoming train.
About 70 people suffered horrific injuries as the front section of the moving train was ripped open and completely destroyed.
It took hours for the hundreds of emergency service workers to cut people out of the wreckage.
John Bowis, who was the MP for Battersea at the time, said he drove to the “awful scene of carnage” as soon as he heard the news.
“It was something you never forget,” he said.
Mr Bowis said the boys from nearby Emanuel School were “impressive” in the way they came to help the injured, but added: “I’m very conscious that some very young eyes and minds were confronted with awful things.”
At 11:00 on Wednesday, in the main remembrance event for survivors and families, bosses from the Met Police, London Fire Brigade, London Ambulance Service and Network Rail will lay wreaths and hold a minute’s silence at a memorial to victims in Spencer Park, Battersea, before a service at St Mark’s church.
The train drivers’ union Aslef will hold a separate wreath-laying event and two-minute silence at the Spencer Park memorial at 08:13, to mark the exact moment the crash happened.
Although many of the Hidden report’s 93 recommendations were acted on, a rail accident report last month found lessons learned in the disaster were being “forgotten”.