On a freezing morning in November 1939, all the Jews in a small Polish town were ordered to assemble in the school.

The 2,300 men, women and children from Ozorkow were then told to strip naked and were stamped on their chests with either the letter A or B.

Bob Obuchowski was 11 and, together with one of his sisters, and 200 others, was given the letter A.

Bob, of Leigh Avenue, Redbridge, said: “Being so young we were making jokes about being either an A or B, then they took the babies and threw them into a lorry from the second floor window. We didn’t joke anymore.”

Everyone given the letter B, including his mother, father and remaining sister, were then herded into lorries and gassed to death.

“My sister Malka had a red mark under her eye and that was enough to kill her,” said Bob. “When we looked at the people who were left we knew it didn’t mean good, it was young people like myself and fit people.”

After the initial sorting in Ozorkow the survivors were marched to a ghetto in Lodz.

Ghettos were sections of towns fenced off with soldiers stationed around the perimeter.

Inside, captives had to use a different type of money, were forced to live in cramped conditions and were kept close to starvation.

“If they saw anyone ill they took them away,” said Bob.

“I got meningitis, which rotted a chunk out of my leg. My sister had to work or we wouldn’t get her rations.

“You were given food for three days but it had to last you eight. People were just dying from starvation.

“They ripped up the floor boards and burned furniture to make fire as it was minus 35C.”

About 75,000 people lived in the ghetto in Lodz, which had its own SS building. People who entered it would never be seen again.

A Jewish mayor would try to negotiate the number of men taken away.

Bob said: “You could see people just lying down and dying, some people ate grass and got dysentery.

“You could put the most precious jewels on the table but the food you had to lock away in case your mother or brother ate it. A bite was a day’s life.

“When someone died they hid the body for a while so they could get their rations. We weren’t human anymore.”

Bob stayed in Lodz for more than three years until the ghetto was closed and its inhabitants were loaded into cattle trains destined for Auschwitz-Birkenau.

Once off the train they were stripped naked and inspected again. This would be the last time he saw his sister Gittol.

Bob had a large dent in his leg as a result of the meningitis and if this had been spotted he would have been immediately executed.

Then came what he describes as “miracles”.

“The boys standing near me moved closer, hiding my scar,” he said.

“It was all miracles that I survived.”

Out of the hundreds of people, Bob was chosen along with 24 other boys to survive.

“We were moved to one side and on the other people were marching to the gas chambers,” he said.

He was then branded with a number on his arm, B-7650, and marched to Auschwitz-Birkenau.

He said: “A few blocks from my own they were shooting people morning, noon and night. More than 20,000 people were shot – my ears were ringing all the time from the noise.”

Bob was then moved from camp to camp, spending time in Babice and finally Rehmsdorf, which he describes as “hell on earth”.

“When I got there I wanted to lay down and die, I was literally dying,” he said. “I had broken my foot at work and the inmates put a cast on it.

“The next morning a Hungarian Jew came in and dragged me and another boy out to go to work and we said what a terrible man he was to make us go to work.

“I managed to struggle back to the camp afterwards and it was empty. He had overheard the guards saying that they were going to clear the camp. Everyone had been gassed.”

At the beginning of 1945, the war started coming to and end and 2,775 survivors were rounded up and marched to Czechoslovakia to be gassed.

“They didn’t want to leave people like me as evidence so they built two big gas chambers in Czechoslovakia and gathered people from all the camps,” said Bob.

“By the end of the march, 75 of us survived. We were just wearing stripy pyjamas – no shoes, socks or underwear. It was minus 30C so most of them just froze to death.”

On May 8, 1945 the group was found by the Russians.

The British government then announced it wanted to bring 1,000 of the surviving children to the UK.

They could only find 700. Bob was in the first group brought to Windermere.

He said: “I was brought back to life. The Russians and English were so kind and gentle with us. We had never been to school or had parents – we were a bit wild.”

He later went to Gateshead to study furniture upholstery, a career he continued until he retired.

At 22 he married Marie, another Holocaust survivor.

They had two children, five grandchildren and two great grandchildren.

Although in his 80s, he spends most of his time travelling to schools telling them his story.

“I try and teach the young people that bullying and starting on others cannot be right and they should always help and defend people,” he said.

“If you see someone being bullied you must go and try and help them, regardless of who they are.”