The centre succeeded an interrogation unit at Diest in Belgium, ran under War Office authority with a mix of military and intelligence officers, and was commanded by Lieutenant Colonel Robin Stephens, who had spent the war running MI5's interrogation centre at Camp 020 outside London. Its original brief was to hold and question former SS, SA and Gestapo men in British custody. Within a year that had shifted. The Cold War was arriving faster than de-Nazification was finishing, and the cells began filling with people suspected of spying for the Soviet Union - Germans, but also Russians, Czechs and Hungarians. One detainee left an account of it. Werner Dankwort had headed the political department of the German legation in Stockholm from 1939 to 1945; he was held here across most of the centre's existence and wrote down what the days were like, and his memoirs sit in the archive of the German foreign ministry in Berlin.

That winter was the coldest Europe had seen in living memory, and it arrived on a continent with no coal to spare. In January and February 1947 prisoners were transferred from No. 74 to the civilian hospital at Rotenburg, near Bremen, arriving with frostbite, malnutrition and injuries. Two of them died. The British medical and military staff who received them were shocked enough to complain up the chain, and senior Army officers responded by bringing in an outsider: Inspector Thomas Hayward of the Metropolitan Police, sent to Germany to investigate British soldiers. What Hayward assembled became a list of specific allegations - prisoners doused with cold water, deprived of boots, set to scrub cell floors without pause in unheated rooms. A former interrogator would later testify that some of the Army warders at the camp were themselves ex-convicts. The centre closed in July 1947.

Four officers were charged; three came to trial between March and July 1948, and all pleaded not guilty. Lieutenant Richard Langham, a German by birth serving in the Royal Armoured Corps, faced two counts of disgraceful conduct of a cruel kind over two former SS men suspected of organising acts of terrorism. The prisoners described beatings, lit cigarettes used on them, cold water and threats. A sergeant told the court he had been ordered to drive one of them around his cell for about two hours; a lance corporal said the reason given was that the men belonged to an organisation planning a rising on Hitler's birthday. Langham's counsel argued that nobody had tied him personally to the 'curious things' that had admittedly happened, and on 31 March 1948 he was acquitted. Captain John Smith, the camp's doctor, went before a court in Hamburg on 7 April facing two counts of manslaughter and eleven of professional neglect. Smith described Bad Nenndorf as a 'bestial hole' full of people who, he said, were being brutally treated without his knowledge; he was cleared of manslaughter, convicted on five neglect charges, and dismissed from the service. Stephens went last, in June. The cruelty charges against him were withdrawn on the opening day, most of the evidence was heard in closed session, and on 20 July 1948 he was acquitted on everything.

Three months after Bad Nenndorf shut, a purpose-built interrogation centre opened at Guetersloh, staffed largely by the same interrogators - which caused visible unease in London. The Foreign Office minister Frank Pakenham demanded that 'drastic methods' not be used. The Army's position was that the standards applied in British prisons did not apply to Army interrogation centres in Germany. There the matter rested for nearly sixty years, until the Guardian obtained the file and published in December 2005 and again on 3 April 2006, printing photographs of prisoners reduced to skeletons. A short, sharp row followed in both countries, with the obvious line drawn to the detention scandals then in the news. Then came the part nobody wanted. From 2006, far-right groups began holding annual 'mourning marches' at the Wincklerbad, using the men starved in those cells - some of whom had served the SS and the Gestapo - as a prop for the argument that everyone's crimes cancel out. Thousands of police were needed each year. The town answered with a movement of its own, Bad Nenndorf ist bunt, which turned out against the marchers every time; the marches ran until 2015 and after 2016 could not be staged at all. Both things stay true. What was done in those cells was wrong on its own terms, whoever was in them.