A silence has been held to mark the time of the accident at the crash memorial site high above the railway line at Ladbroke Grove in west London on Saturday.
It was followed by a service at St Helen's Church in North Kensington, where 31 candles - each bearing the name of one of the deceased - were lit alongside a 32nd candle for all the survivors.
Just before 8.10am on 5th October 1999, a rush-hour train collided almost head on with a London-bound high-speed train which was heading for Paddington station.
The Thames Trains driver, Michael Hodder, 31, and the First Great Western (FGW) driver, Brian Cooper, 52, were among those killed as the collision led to a fireball in which coach H was burnt out.
As well as the fatalities, more than 220 other people were injured, including Paddington Survivors Group chairman Jonathan Duckworth, now 61, from Stroud in Gloucestershire.
Today we remember those who perished 20 years ago at Ladbroke Grove. We hold in our hearts the memory of those who never returned home that day & who bear the scars, both physically & mentally. The survivors, bereaved and the emergency services & the Chaplains who supported them. pic.twitter.com/1bGt7SRW2A— Liam Johnston (@railwaychaplain) October 5, 2019
Travelling on the FGW train, Mr Duckworth said he was left "battered and bruised" after being thrown around the carriage during the crash, and later he was diagnosed with post-traumatic stress disorder.
The former shopping centre manager told the PA news agency that the crash had changed the lives of so many people caught up in the disaster and its aftermath.
He added: "It is a desperately sad day for the bereaved because it is such an unnecessary day - the crash should not have happened.
"There were lots of factors that could have stopped it, none of them had been put in place.
"My life was completely changed. My world was literally turned upside down, it was turned upside down in the coach and turned upside down now."
20 years ago today 31 people lost their lives at the Ladbroke Grove train crash. Remembering with families, survivors, emergency services this morning. Memories still live, emotions still raw. @dioceseoflondon pic.twitter.com/WJEyn1nwgA— Graham Tomlin (@gtomlin) October 5, 2019
No words can express the sorrow felt by so many people following the Ladbroke Grove disaster pic.twitter.com/jMrbVMGzgR— Liam Johnston (@railwaychaplain) October 5, 2019
The subsequent inquiry into the disaster revealed that the Thames service travelling from Paddington to Bedwyn in Wiltshire had gone through a red signal before crashing into the London-bound high-speed FGW train which had left Cheltenham Spa in Gloucestershire at 6.03am.
HM chief inspector of railways Ian Prosser said it was very important to mark the anniversary of the tragedy because so many people were killed, injured or affected by it.
But he warned that while the disaster had a "profound" impact on safety it was vital the rail industry did not become complacent about passenger safety.
He added: "Ladbroke Grove had a profound affect on ensuring that improvements were made to railway safety, that's also why it is important to remember the anniversary and the changes that have resulted from it that have had a very positive impact.
"It is very important that we remain vigilant and therefore don't become complacent.
"The railway now is busier than it has ever been.
"It's important we don't lose sight about what's happened."
Mr Duckworth, who now runs his own business, said the anniversary was important because people might forget the disaster and let safety standards slip which could lead to another tragedy.
He added: "There is no doubt that the railways are significantly safer than they were 20 years ago, it was a dreadful time for the industry.
"It is really important to remember what happened 20 years ago to reinforce that the changes that have happened since then have been fantastic and must not slip because if they slip more people will die and more people's lives will be completely transformed."
Tony Thompson, the memorial committee coordinator, said that while there were around 600 people on the trains, the disaster had affected thousands.
Mr Thompson, who was a superintendent at British Transport Police at the time of the incident and spent two weeks at the crash site, added: "Disasters are all about people and it is really important that we recognise the fact that so many lives were lost and so many lives were affected.
"This was the second largest disaster in the UK since the war, it was one of the worst train crashes we have had.
"There were 600 people on the trains but it has affected the lives of thousands."
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