Amid the deepening horror of March 1939, as Europe stood on the precipice of a Second World War, it was no wonder the arrival in Britain of 20 Jewish children by aeroplane from the Czech capital Prague should pass almost unnoticed.

Five days later, on March 15, as German troops marched across the border, Hitler’s Foreign Minister Joachim von Ribbentrop told the world: “The lands of the former Czechoslovakia… are from now on part of the Greater German Reich.”

Trevor Chadwick, the only adult to have escorted the children recalled how they “were all cheerfully sick, enticed by the little paper bags, except a baby who slept peacefully in my lap the whole time”. The youngsters, believed to be between the ages of two and 12, had been evacuated to the UK in the nick of time by the British Committee for Refugees in Czechoslovakia (BCRC).

The organisation would go on to save hundreds of Jewish children from persecution and almost certain death at the hands of the Nazis. And this was in large part thanks to its most famous member: Nicholas Winton – often described as Britain’s Oskar Schindler after the German industrialist credited with saving 1,200 Jews – who took charge of its children’s section.

Yet in fact, despite his very great fame, Winton’s efforts were even more profound than is currently recognised. There were several other transports, including the aircraft carrying 20 children flown out of Czechoslovakia and into Britain with Chadwick, which have never been credited to Winton – despite the fact he organised them. In fact, I can reveal that the true number of lives saved by Winton is closer to 700 than the 669 figure he is credited with.

Now the subject of the major new big screen biopic, One Life, Winton is portrayed excellently by Johnny Flynn and Sir Anthony Hopkins at different stages of his life.

Hopkin’s Winton follows his retirement in the 1980s, where he contemplates what to do with a scrapbook containing the details of the 669 children he evacuated on eight trains from Czechoslovakia to England between March 14 and August 2, 1939.

Flynn plays Winton as a young man in 1939, who was ably supported by the free-spirited and self-assured British man Trevor Chadwick, played by Alex Sharp. The film’s name comes from a passage in the Jewish text, the Talmud, “Save One Life, save the world”, which was engraved onto a ring presented to Winton by those he rescued.

Although he is credited with saving far more than just one life, the extent of his efforts has never been truly recognised.

Winton’s achievements only became widely known after he was invited onto Esther Rantzen’s show That’s Life! in 1988. Live on television, the wartime hero was reunited with many of the men and women whose lives he had saved by organising homes for them in Britain nearly half a century earlier.

It was the moment it was revealed he was unknowingly sitting next to three of those 669, none of which he had met before. And in which they learnt for the first time who was responsible for saving their lives – and got to say thank you.

“Is there anyone here who owes their life to Nicholas Winton?” Rantzen asks the audience. “If so, could you stand up please?”

Immediately, the rows around him all silently rise with glowing faces of utter gratitude. Nicholas, who was knighted in 2003 for services to humanity, stood and turned in amazement to gaze at the sea of lives he was responsible for.

Born in 1909 in North London, Winton lived with his German parents and two siblings in their comfortable 20-roomed house in Hampstead. Although he modestly later reflected that his family were not “by any means rich (but) I suppose moderately middle class”, his early childhood was undoubtedly comfortable, looked after by four household staff.

After attending the local University College School, a mere three minutes’ walk from their home, Winton moved to the newly-opened Stowe School in Buckinghamshire aged 14.

It was here he learnt to indulge himself in a broad range of hobbies from horse riding and fencing to pigeon fancying.

The school’s headmaster did not seem to mind that Winton flourished more outside of the classroom than within, commenting that his students learnt the skills necessary to be “acceptable at a dance and invaluable in a shipwreck”.

A lesson that, perhaps, did not go amiss as Europe became increasingly dismasted.

After finishing school, rather than going to university, his father encouraged his son to go straight into work so as to support the family financially.

Winton recalled that his father Rudolph “was very keen that I should become a banker” – not a career he aspired to. Outside of earning a good salary, the work as a stockbroker was not especially enjoyable.

However, it did allow him to live in Germany for a year in 1929, where he witnessed first-hand the dire impact of the post-war depression.

Despite this, life could have turned out to be quite mundane for Winton, had he not received a phone call from his close friend Martin Blake at the end of 1938.

Played by Ziggy Heath and Jonathan Pryce, at different stages of his life, in One Life, Blake was a teacher at Westminster School, who had been due to go skiing with Winton in Switzerland to celebrate 1939’s New Year.

The day before their flight, Blake called Winton to say: “I’m going out to Prague tomorrow… Give up your winter sports holidays and come and join me.”

Winton was intrigued, so he changed his plane ticket for the next available seat to Czechoslovakia, arriving in Prague on December 31, 1938.

Here, he encountered the aftermath of the Western powers’ decision that October to sacrifice the Sudetenland – a piece of land bordering Germany and Czechoslovakia – to Adolf Hitler and German control.

The ensuing Nazi rule had triggered a mass exodus of nearly 200,000 refugees, including many terrified Jewish citizens who fled to Prague seeking safety.

Witnessing the dire situation, Winton and Blake offered their assistance to the BCRC, a newly-established organisation led by Doreen Warriner, an English academic who had already spent three months aiding those suffering in the freezing conditions, having fled their homes and jobs to escape persecution.

Although in One Life, Romola Garai portrays Warriner as the cautious and almost reluctant member of the group, she was in fact the driving force who initiated the whole rescue effort.

Impressed with Winton, she soon appointed him Secretary of a Children’s Committee.

Despite having only three weeks before returning home, Winton worked tirelessly on the daunting task of evacuating unaccompanied children from Czechoslovakia.

He collected details of Jewish children and compiled a list of 5,000 children whose parents sought their safety.

Knowing that they would not be allowed to leave the country together, parents were desperate to save their children, even if it meant being separated from them.

As his stay in Prague concluded, Winton returned to Britain in January 1939, armed with a file containing the children’s details. Trevor Chadwick took over operations in Prague, while Winton, along with a team in London, including his friend Martin Blake, worked to find families willing to adopt the youngsters.

He was helped throughout by his determined mother, Barbara Winton, depicted magnificently in the new film by Helena Bonham Carter.

Balancing his day job as a stockbroker, Winton dedicated his evenings to this humanitarian effort, writing hundreds of letters to potential foster parents and seeking funding from donors, often while dealing with the logistical nightmare of organising British visas for the children.

A month after leaving Prague, Winton and his mother stood on the damp platform of London’s Liverpool Street station with dozens of foster parents, as a huge green train carrying the first 20 children pulled in.

Winton personally introduced each child to their new families and watched them leave to start their lives in England.

This became a routine for Winton and his mother over the next six months, with each train containing more and more young passengers, the largest carrying 241 children left Prague on July 1.

“I really don’t quite know how we managed to sort the chaos which ensued when the train pulled in,” he later reflected.

In total, 669 children escaped Prague on trains, but the several air transports of children also organised by Winton seem to have slipped through the fingers of historical record.

Following the first flight on March 10, 1939, Warriner wrote in her diary that “Winton began to get his children’s transports going and flew off with planeloads of Jewish children”.

In fact, as I discovered while researching my new biography of Sir Nicholas, at least three aircraft, each carrying 20 children, made the trip from Prague to the UK at the behest of Winton, meaning at least another 60 children were saved.

After Britain’s declaration of war against Germany on Sunday September 3, 1939, all transports to the UK were halted.

Some 15,000 Jewish Czech children not lucky enough to get a place on the planes or trains organised by Winton were subsequently sent to concentration camps. Only 93 would survive the war. It was a tragedy, and one that stayed with Winton until his death. His later reluctance to discuss his actions in 1939 wasn’t solely due to his modesty; it also stemmed from an overwhelming sadness for the children he couldn’t rescue.

This guilt Winton felt at not saving more children – which stayed with him until his passing at the age of 106 in 2015 – is beautifully depicted by Hopkins, especially over the 251 youngsters who were sitting on a train on September 1, waiting to depart from Prague. Germany’s invasion of Poland that day meant that the transport was cancelled and most of the children would go to perish in concentration camps.

One Life beautifully depicts Winton’s character – an emotional and understated man with huge determination and an excellent sense of humour. Living by his motto – “If something is not impossible, then there must be a way to do it” – he was able to save, with others, the lives of hundreds of children.

His story echoes down the generations and will now find a new audience thanks to One Life. So we can continue to be thankful for Nicholas Winton.

• The British Oskar Schindler by Edward Abel Smith (Pen & Sword, £20) is out now. Visit expressbookshop.com or call 020 3176 3832. Free UK P&P on orders over £25