Steven Frank learned a salutary lesson at the age of eight in Westerbork transit camp.

“Wandering on my own, suddenly I found myself right up against the barbed wire fence, about six feet high with a moat the other side. About 20 metres away, there were two German guards with an Alsatian dog. I froze. I looked at them and they looked at me — and then they unleashed the dog.

“The dog came snarling towards me. I put my hands in front of my face. I was bitten all over my arms, my thighs and my legs and I can still hear the German guards laughing at this bit of Jew-baiting. I ran back to the barracks, bleeding from all these bite marks.

“But after that, I’d learned my lesson. When I got to a corner I would look before I proceeded. If I saw guards I’d keep well away.”

Mr Frank was born in Holland, where his English mother had met his father, Leonard, while attending finishing school. He was five when the Germans invaded.

Leonard Frank was a prominent young lawyer in Amsterdam, “very much involved with people who weren’t as fortunate as we were. One of the reasons he probably never left Holland was because he was on the board of a famous Jewish mental hospital in Amsterdam and he realised that if the Germans invaded, these people hadn’t a clue what was going on and he really needed to help protect them.”

He joined the Dutch resistance, helping Jews escape to Switzerland via France. “And then one day he was betrayed,” his son recalls.

He was eventually taken “to the big prison camp at Amersfoort, where he was tortured, and from there, in very poor physical condition, he was sent to Westerbork. Not long after that he was put in a cattle truck and sent to Auschwitz, where he was gassed [aged 39] on January 21, 1943.

“My mother, showing enormous courage, found out when he was in Amersfoort who the cleaners were, and actually went into that prison disguised as a man, scrubbing the floors — and briefly spoke with my father. He told her that he had been tortured but he hadn’t given anything away. That was the last she saw of him.”

Three of his father’s non-Jewish friends “wrote a long letter about all the organisations he had been involved in and the people he’d helped.”

It led to Steven Frank, his two brothers and their mother being added to the Barneveld Group — a list of prominent Dutch Jews originally interned at Barneveld castle.

However, after six months there, “the German Army stormed in and they sent us to Westerbork. That put the fear of God into everybody because Westerbork was where most of the Dutch Jews went before they were carted off on trains eastwards.

“It was in Westerbork that one began to realise things were really bad. The food was adequate but monotonous, there was lice everywhere, scarlet fever, dysentery, polio.”

But things would get worse. In September 1944, the family was moved to Theresienstadt, near Prague — “39 hours in a cattle truck, no food, no water, no sleep. In our cattle truck there were four tiny little slit windows and we would clamber up on rucksacks to get air.”

A garrison town, Theresienstadt was built to house 8,000 soldiers. The Germans forced 44,000 Jews into the same space.

“My mother volunteered to work in the camp hospital laundry, where she would wash the bandages and swabs.

“Nothing was sterilised, everything was reused. But they did have hot water there and when the authorities weren’t looking, she would wash clothes because the only way to keep typhus at bay was to keep yourself as clean as possible. She would barter that [washing] for food.”

Mr Frank and his two brothers were put in a “children’s home” within the camp. When the Nazi guards came in, “they weren’t interested in me, I assume because I was in the Barneveld group.

“For the rest, if there were two sisters they would take one and leave the other behind; if there were two brothers they would take one and leave the other behind — one lot going to Auschwitz, another lot staying behind.

“All these children had left were one another and the Germans deliberately broke that last link. That cruelty still riles me today.

“As we moved into 1945, instead of leaving Theresienstadt, transports were now coming back in, mainly from Auschwitz. Cattle trucks, mostly open cattle trucks, with corpses inside. My mother would go through them looking for my father. The few who survived were taken to the sort of hospital we had — and then we heard about the gas chambers, because these people knew.

“We were really frightened.”

The Nazis forced their prisoners to help them dispose of evidence of their crimes.

“We children were woken up very early one morning and taken to the crematorium. We were lined up in this dimly lit tunnel and told to hold hands and stand in a row. For hours and hours, we were passing little boxes from right to left.

“Each box contained the ashes of the dead. And the Germans, with true efficiency, had labelled each box with the name, date and place of birth and date and place of death.

“And as it came down the line, a child would recognise their mother —or their father, brother or sister — and would quietly sob. You could hear this quiet sobbing all around. The Nazis were throwing these ashes into the river, to get rid of the evidence before the Allies arrived.”

Of around 15,000 children sent to Theresienstadt, just 93 survived. The camp was finally liberated in May 1945 and Mrs Frank managed to convince the Swiss Red Cross and American and British officials in Europe to allow her and her three sons to travel to England, where her father was living.

Learning English at the age of 10, Steven Frank went on to become a chemist for a company looking after water supplies, marrying and raising a family.

He began speaking in schools in 1995 and has now addressed more than 800 groups of students.

“I’ve been doing this for so long I come across teachers, now heads of departments, who say: ‘I heard you speak when I was in year nine’. But I will go on doing it because that is what God wants me to do.

“Some of the reactions you get are quite extraordinary.” A week after speaking at a school in Sutton, he received an email from a teacher, who wrote that a girl who had asked a question was “a selective mute and that was the first time she had ever asked a question in school”. It made Mr Frank think that if his talks could make such an impact, he must be doing something good.

He supports the planned Holocaust Memorial next to Parliament but strongly opposed Sunday’s burial service for the remains of six Holocaust victims at New Bushey Cemetery.

“I think these bones and ashes should have been left in peace. How do you know that they’re Jewish? How do you know they’re religious Jews?”

Although “very proud of the race I belong to”, the Hertfordshire resident is not particularly religious.

However, he “first really took on board the enormity of being a witness to the Shoah when in Northwood and Pinner Liberal Synagogue, where two of my grandchildren were having their barmitzvah and batmitzvah.

“The rabbi said to them: ‘You have a very important legacy; your grandfather was a Holocaust survivor. It’s very important for you to remember that.’

“I suddenly thought: ‘I’m a witness to one of the major traumatic pieces of history that’s happened to our people. That is a huge responsibility to carry forward. That’s why I feel it’s important that I go on telling the story.”

Mr Frank also recalled how, as he, his brothers and mother were leaving their home in Holland, their Catholic nextdoor neighbour came to say goodbye.

“She gave my mother a little black silk purse. She said: ‘Take this — it may be of some strength on your journey ahead.’ What she gave my mother was a Jesuit crucifix. My mother carried that crucifix with her throughout her life. And when she died I found it and I use it in my talks,” not least because what occurred on arrival at Theresienstadt.

“We were taken into a brightly lit room to be interrogated [by a female German guard]. This woman oozed with hatred. And her manner was very, very frightening. My mother had to turn out her handbag. And out fell that little black silk purse with that little crucifix in it.”

Speaking to the guard in German, his mother asked the guard not to take the crucifix. The guard returned it. “In that glimpse of compassion, that brief glimpse of compassion in that evil woman’s eyes, for me there was God.

“I never saw God again.”