Lisa Potts: Why we owe her the greatest debt, by the little ones she saved from the machete horror at St Luke's

Each has since displayed his or her own brand of courage to overcome the trauma and find success.

Fran and Ahmed were, respectively, four and three years old when machete-wielding Horrett Campbell ran amok at St Luke's School, Wolverhampton 20 years ago today.

Now grown up, both hold impressive university degrees and have embarked on substantial careers – one as a hospital psychology assistant and the other as a problem-solver at a healthcare company.

Read more: Why Lisa Potts forgives attacker Horrett Campbell

They remember little or nothing of the bloodbath that stunned the nation but the scars, both mental and physical, have been a constant reminder of how closed they came to death – and how much they owe to the nursery nurse whose extraordinary valour kept them alive.

Unlike them, Lisa Potts has total recall of the attack that left her seriously injured. Every detail of those terrifying eight minutes of violence is indelibly etched on her memory.

Now a 41-year-old mother of two working as a health visitor nurse working in the community, she recalled: "Campbell came towards me and cut me straight across the left arm. I didn't feel any pain. I think the adrenalin was pumping round my body.

"Francesca was right next to me because I had children holding on to my skirt in fear not realising what was going on. I remember the knife coming down as if it was going to hit Francesca on the neck. I put my hand across her face and he cut her straight across the face, neck and ear."

Lisa continued: "Ahmed came running towards me with his sister. I tried to pick him up, his sister was screaming, and as I picked him up Campbell cut me across the right hand and straight across Ahmed's head.

"I grabbed Ahmed and pushed him inside the school with the other children. The man was behind me and in the doorway with me. I did not realise that I could not shut the door because my right hand was so badly injured.

"As I tried to shut the door his foot was in the doorway. I was stuck in a very small corner with dressing up stuff and toys.

"The door facing me led to a classroom with another 30 children inside. I tried to get into that classroom.

"I had got all those children in front of me and he hit me across the back, twice.

"I remember grabbing as many children as I could and, as he turned round, I started running with all those children to get out of the main building.

"The last blow I felt was right across the back of my head which is when he fractured my skull.

"I continued to run and looked back to see where he was.

"At that point he put away the machete, jumped the fence and was gone. He was not found until 48 hours later."

Fran – left with a scar from ear to mouth and two metal plates holding her jaw together – is training to be a clinical psychologist in the hope of stopping mentally damaged people from committing similar outrages in future.

Now aged 24, still living in the West Midlands, and, like Ahmed, talking publicly about the ordeal for the first time, she confessed: "It has been difficult living with the scar. It does get to me at times but I am just grateful to be alive. I owe my life to Lisa. "I can't remember anything about the incident except him standing there. It doesn't seem real. It feels like a story. I did not forgive him for what he did to me and the others for 18 years. Then I realised that the best thing to do was to forgive him and get on with my life."

She continued: "As a teenager I ignored the whole situation and didn't want anything to do with it. I didn't speak about it at all. I tried to repress it as much as I could until it physically got to me. I went to talk to Lisa about how I felt last year because I was really struggling.

"I was in such a dark place after suppressing my feelings for so long. People tell you that they know how you feel but they don't.

"The only person who did was Lisa because she knows exactly what went on. She had lived it. We have a connection like a sisters' bond.

"I was interested in psychology before I really knew what it was but the more I knew about it the more interested I became. As I got to the stage of careerchoices I realised I had to sort myself out and come to terms with what had happened to me."

The psychology graduate, who is currently working as a hospital psychology assistant. concluded: "I want to help prevent people with mental problems doing the sort of thing that Horrett Campbell did.

"I want to offer support to people who have mental health problems or emerging problems before it escalates into something horrific.

"At the same time I want to work with people who have experienced violence to assist them in coming to terms with what has happened. My motivation is that I do not want others to go through what I have had to endure." Ahmed was on a taster day at St Luke's School – where his sister Mariam, now 24, was already a pupil – and received a fractured skull and slash wound to his right elbow in the attack.

He graduated from Aston University last year with a masters degree in electrical and electronic engineering and now works for a healthcare company based in Hampshire.

He is on the team that identifies the cause of any problem with the product and provides a solution. Aged 23, he said: "I am not sure if I remember what happened or simply recall what other people have told me about the incident.

"I still get migraines but far less frequently than when I was younger. I have one every few months now. I also had nightmares when I was younger."

There are scars on his head and right elbow. He ensures his hair is long enough to obscure the former and is vague if people ask how he got the latter. I tend to just brush off any questions about the scar.

"It is not because I feel weird or ashamed about it, I am just more comfortable not talking about what happened.

"I am not hung up about it. I just can't be bothered going through it all. Would people believe me if I did? I can go for days or weeks without even thinking about it but it is always at the back of mind."

Ahmed went to a different nursery for a short time but soon returned to St Luke's where teachers, including head Denis Bennett, were aware of what had happened to him.

"I was not isolated but was definitely treated differently. It didn't affect me much."

Ahmed went on: "I don't have any feeling of ill will towards Horrett Campbell.

"He had mental health issues. I have seen a report in a newspaper from the time that carried a big picture of him under the headline 'Face of Evil'.

"That made me angry. It did not take the issue of mental illness seriously. He was not evil, he was ill and was not fully aware of what he was doing."

He added: "It feels weird thinking about my sister and the other children who were there when it happened but were not physically hurt.

"Obviously Lisa is a very special person to me.

"She saved my life and that is the greatest debt you can owe."