Children seeking sanctuary in Britain before the Holocaust were refused the lifeline of the Kindertransport if they were thought to have disabilities or looked too Jewish, say researchers.

Historian Louise London, who has written about Britain’s immigration policies at the time, said that it was “the Jewishness of Jewish refugees” that was seen as “particularly problematic”.

Speaking at a conference on Monday organised by the Association of Jewish Refugees to mark the 80th anniversary of the Kindertransport, Dr London said it was thought that Jewish children separated from their parents “would be less visibly Jewish” and, once dispersed into British families, “over time they would be, as was often said, ‘Anglicised,’ hastening their assimilation.”

She added that the “problem of what to do with the Jews took precedence over efforts to save them”.

One document featuring details of a 15-year-old refugee from Vienna, Kitty Milch, stated she was “an intelligent looking and not particularly Jewish young woman”.

Professor Paul Weindling of Oxford Brookes University, who has studied letters sent by the Kindertransport office in London and organisations applying to accept refugee children, said it was also common for people to request “non-Orthodox” children so that, it was thought, they could be more easily integrated.

“People were specifically requesting what type of child they would like.”

Medical certificates issued to children at the time guaranteed that they were “fit for work” and confirmed that there was “no record of family illness, disability, or poor mental health”.

He said he knew of a case of one child having to travel to the Nazi medical centre in Vienna to get her certificate. “You can only imagine how scared she would have been,” he said. “Others failed and were rejected.”

Children who were rejected often ended up dead, he said.

Fourteen-year-old Eva Renee Seinfeld wrote to Princess Elizabeth from Vienna appealing for help in July 1939, but by that point the number of children coming to Britain from the city had shrunk to 291.

“May it please your Royal Highness to grant my request in assisting my great despair and to make it possible to come over to England,” she wrote.

“I am of a quiet and modest kind, of a good and severe education and it will be my greatest endeavour to be worthy of your noble and kind protection.”

She was deported from Vienna in 1942 and died in Sobibor.

Heinrich Steinberger applied to be reunited with his father who was in Kitchener camp near Sandwich, Kent, in August 1939, but by that point the number of children granted permission was down to 195.

Mr Steinberger, whose mother had a domestic permit to work in Britain, was not successful. Records show he was deported from Vienna in 1942 and died in Sobibor.

Prof Weindling found that mental and physical characteristics were often referred to in the correspondence. He said the head of the main Kindertransport organiser in the UK, the Movement for the Care of Children from Germany, requested children who were “bright,” “physically fit” and possessed “exceptional qualities”.

He said: “They were specifically looking for intelligent, healthy children, possessing positive moral qualities and specifically stated that they did not want those who were mentally or physically disabled.”

He also gave the example of Hans Lang, born in 1932 in Vienna and in the care of the Jewish Boys Orphanage. He was described on an application as “very well behaved but very slightly mentally backward.” His application was rejected by the Kindertransport office in London and his fate was unclear.

Prof Weindling said organisations which funded the Kindertransport sought to ensure that none of the refugees would become a financial burden on the public, as well as applying pressure for children to be selected based on their intellect and appearance.

He said 2142 children were sent to Britain from Vienna between December 1938 and August 1939 but after the 851 sent in December, numbers massively decreased.

Children were often required to produce medical and school certificates and social workers were instructed to carry out home visits to ensure each child’s suitability, his research shows.

Officials in Vienna received “frequent requests” for orphans, because host families in Britain wanted to take in young children.

Dr London said there was an “obvious” tension at the time between British government policy, which was that children brought over should re-emigrate, and the desires of “foster-parents for a child that would become a permanent member of their family.”

She said: “The government made no effort to resolve these ambiguities.”

Every child was required a guarantee of £50 to finance their eventual re-emigration as it was assumed at the time that the danger was temporary, and the children would return to their families when it was safe.

“Without their parents the children were acceptable here,” Dr London said.

According to Dr London, author of Whitehall and the Jews, it was thought that “if some were ultimately allowed to remain, they could contribute good white stock to the population at a time when the birth rate was low.”

Prof Weindling said the research deconstructs the “myth” of the Kindertransport as an unproblematic rescue mission.

Children often took it upon themselves to apply to be let into Britain. Prof Weindling said it was an example of the initiative they had to show at the time but not everyone would have been able to express the same tenacity.

For example Otto Hutter, who was 15, enrolled himself on the Kindertransport in December 1938, the month the first Kindertransport from Vienna departed.

Mr Hutter recalled how he joined a short queue of accompanied children and was interviewed by officials.

“Regardless of my having presented myself without a parent, I was enrolled because - as I learned much later - boys nearly 15 years old were given priority lest they be soon sent to forced labour camps.”

Mr Hutter said he was made to undergo a medical examination before being issued with documents for his parents to sign and was sent away with a list of clothing to pack into a small case.

A letter written by Mr Hutter recalled: “I was issued with an identification number printed on a card to be worn around the neck when joining the transport due to leave in less than a week’s time. My number was 359. Just 360 children were enrolled that day. So I had made it just in the nick of time.”

Hella Pick, journalist and Kindertransportee who arrived in Britain in March 1939, said there was a lack of awareness around the conditions placed on refugees at the time and more needed to be learnt.

Ms Pick, who was as born in Vienna, Austria, into a middle class Jewish family, said researching her own story and the process in which she arrived had been a “rapid” learning experience.

“It has made me realise how fortunate we were to be selected. Had we come from some other background we might not be sitting here,” she said.

She said strict restrictions on refugees were “sadly” symptomatic of the country’s current “attitude to immigration”.