The exhibition, which traces the origins and course of the Nazi extermination programme, includes diaries, documentary artefacts and photographs. Perhaps the most moving evidence of the genocide, however, comes from the video and audio testimony of 16 survivors, played to visitors at certain points in the display. Dobias was among the first to be recruited – coming to the curators’ attention through his gift to the collection of a metal concentration camp bowl which he had kept since the war. His story was as follows.

He was born on June 3 1913 in the Bohemian town of Turnov, close to Prague, where his father, Frantisek, owned a chimney-sweeping business. Already fluent in German on account of his schooling in Liberec, which had a thriving German population, the teenage Prem spent a year at a school in Hildenborough, Kent, gaining the confidence to start offering private English lessons in Prague. With the money he saved he was able to study for a year at the University of Grenoble. His fluency in languages would later be crucial to his survival in Mauthausen concentration camp.

Dobias enrolled at the ancient Charles University in Prague to read Law, but his studies were interrupted by the German dismemberment of Czechoslovakia. Jews had to wear yellow bands bearing the Star of David, and were ridiculed by German soldiers. As some attempted to flee, Dobias – not Jewish himself – was able to draw on his friendship with a civil servant in London to provide assistance, and became part of a group with an escape-line across the border to Slovakia and from there to Italy or Hungary. Unfortunately, one escaper was arrested and the name and address of Dobias’s London contact were found in his notebook. A Gestapo patrol was sent to arrest Dobias, seizing him as he played cards with his family just before Christmas 1941.

He was taken first to the local prison in Turnov and from there to Ruzyn (part of Prague); then, in May 1942, he was sent to Terezin, the infamous fortress turned internment camp. From there he was moved to Mauthausen, where he was forced to work in the granite quarry, enduring the starvation rations (Dobias added nettles to his food for extra vitamins) and constant beatings that were responsible for a high death rate among fellow prisoners .

Keenly aware that the plight of Jewish prisoners was worse than that of political prisoners like himself, Dobias did what he could to try to improve their situation with gifts of food and – on one occasion – an effort to protect a young Jewish boy by hiding him in the camp’s dental surgery. Dobias was haunted by a particularly cruel episode when the inmates were invited to volunteer for pig-feeding duties. It turned out to be a ruse to provide a pretext for shooting them.

Dobias was used by the Nazis to test experimental vaccines, and at one point was selected to be killed in a gas van which operated at Mauthausen. Two Polish inmates, Francziszek Poprawka and Kaziemierz Rusinsek, approached the officer in charge, claiming to have an order from the Commandant to release Dobias because he was needed as an interpreter. The bluff worked, and Dobias was spared.

On May 5 1945, Mauthausen was liberated by American forces. A prisoner — a Russian major — was presiding over a makeshift judicial process. The Americans swiftly imposed their own authority and Dobias became personal interpreter to the divisional commander, Colonel Richard Seibel, and later testified at the Nuremberg trials. It was at this time that he got to know Simon Wiesenthal, the famous Nazi hunter, remaining friends with him until Wiesenthal’s death in 2005 .

Moving to London in 1947, Dobias married Hana Budlovsky, whose grandparents and extended family had been murdered by the Nazis. Hana had found work at Reuters Radio Station, translating the news coming on ticker tape out of Germany. Dobias embarked on a career in the jewellery business, working in Toronto, New York and eventually London.

In 2008 the University of Minnesota Law School established a fellowship in Human Rights in Prem Dobias’s name. Recent recipients have had internships at the International Criminal Court in The Hague and in Tanzania on genocide prosecutions.

His wife Hana died on April 29.

Premysl Dobias, born June 3 1913, died March 27 2012