Former civil servant Richard Jackson made headlines in 2008 when he left top secret files on a train

Warning: This story contains a reference to suicide

It was an ordinary Tuesday train ride to work when top civil servant Richard Jackson made the biggest mistake of his life. By the time he realised, with a sudden jolt of panic, it was too late.

He had left highly classified documents on the train.

The split-second error became national news and Jackson's life was thrown into turmoil. He was consumed by shame and humiliation.

Nearly 20 years on, he recounts that fateful day and the aftermath to BBC Radio 4's Life Changing podcast. He says he is proof that even when you've made your worst mistake you can rebuild your life.

Before his life unravelled, Jackson was 37 and living in Yateley in Hampshire with wife Maddie and stepdaughter Charlotte, 15. His other stepdaughter Becky, 20, was at university.

"We were very happy," he says. "But I was very focused on my career.

"My worth and my value came from that career, job title, position and responsibility.

"I found myself working 100-hour weeks for a while," he says. "I didn't switch off."

He had been seconded from the Ministry of Defence to the Cabinet Office for a job in global terrorism, handling first-hand intelligence from GCHQ, MI5 and MI6.

Leaving his Whitehall office one Monday evening, he swept up a pile of forms to fill in to make his secondment official.

Back at home, he realised that buried within the bundle were "two papers on two classified subjects, and they were both top secret".

In hindsight, Jackson says he should have phoned the Cabinet Office and asked someone to collect the documents securely.

But he puts what he did next down to "maybe a bit of self-preservation".

"Maybe if I get them back, no one else will ever know."

He put the top secret papers in a bright orange cardboard folder and sat on the train the next morning thinking over and over "do not forget this".

He got off the train and walked briskly towards Whitehall. Then he "realised I hadn't got the folder... it just felt for a moment like the world had stopped."

Jackson went to every station the train stopped at and asked whether someone had handed a folder in. Nothing.

"I was frantic. Everything, every movement felt very jerky... I felt sick."

He didn't outwardly break down until he saw Maddie: "I told her I'd ruined our lives. She just held me. She told me it would be all right and we'd get through this."

Richard credits wife Maddie for helping him recover from the worst mistake of his life

At work the next day, Jackson discovered the documents had been found and handed to the BBC.

Jackson says his first sense was "relief in that the papers were back somewhere safe" before the realisation "it was now going to be public".

"I was the main story on the 6 o'clock news that night. And they [the Civil Service] suspended me, pending an investigation."

Richard says he feels lucky to have magical people like stepdaughters Charlotte and Becky in his life

Jackson hid away at home. One lunchtime, Maddie found him sitting cross-legged on the sofa sobbing.

"I'd spent the morning trying to find a painless way to die," he says, "I've often thought what would have happened if she hadn't come home that lunchtime… but I guess I'll never know.

"We spent that afternoon talking… and I think that was the first time where I thought, 'if I'm going to get through this, I can't do it on my own'."

The Cabinet Office found it was an act of gross misconduct and demoted him three grades. He was charged under the Official Secrets Act, avoided jail, and was fined £2,500.

On paper it was over. But Jackson could not shake the feelings of shame, regret and humiliation. He credits the many people who cared about him for helping him piece his life back together. "I fixed very little myself. Lots of people fixed me."

After returning to the MoD in an HR role, then moving to the Department for Culture, Media and Sport to work on the Olympics, Jackson left the Civil Service and worked for the Samaritans. He then took on a role running a team of analysts looking at global terror risk, and started training as a life coach in his spare time.

When he was made redundant, he set up a coaching company, NewDay, which helps people cope with the stress of handling distressing material.

"I could tell my story... and there'd be a point to it. There'd be a reason for what I did."

Richard keeps an evidence board of things he has achieved and kind things people have said to help him remember his success and worth

He wants people to know there is a way back from the biggest mistake of your life.

"You can be in a really bad place, and you can still stand up, and you can get through it and there are ways to help yourself do that and get help."

Asked if he's forgiven himself he says no - but he is happy again.

Maddie is happy too that he no longer works 100 hour weeks. "My life is not defined by my career and I'm more present at home," he says.

"I am much more appreciative of how lucky I am to have magical people in my life."

Richard Jackson has shared steps that helped him move through his traumatic episode:

Get your thoughts out of your head. In a dark place, your mind jumps from "I made a terrible mistake" to "I am a worthless person" at the speed of thought. Writing it down or talking to someone slows things down to give you a chance to notice the illogical leaps.

Continue activities you enjoy. When you feel unworthy, you stop doing the things that lift you up. Work out what they are - the gym, a book, a long walk - and make them non-negotiable fixtures in your routine.

Remember your worth and your success. I keep an evidence board by my desk with notes of things I have achieved and kind things people have said. It's a tangible reminder that I am not that mistake, I am so much more.

Find your critical friend. You need someone who is your cheerleader but will also call you out when you let good habits slip. Anyone who is truly on your side.

Work out what you can fix, and what you can't. If you've caused harm, take responsibility: apologise and put things right where you can. But don't assume responsibility for things that were never yours to carry.

Don't confuse your worst moment with the whole story of your life. You are not that mistake. You are still the person who existed before it, and there can still be a person after it whom you haven't met.

If you or someone you know has been affected by a traumatic experience or is suffering from emotional distress, there is support on the BBC Action Line website.