Jewish newspapers in Britain and America echoed that praise, and Hitler branded him "a Jew lover".

However, his image turned sour in the 1960s, thanks to Soviet antagonism towards the Vatican and a German play by Rolf Hochhuth, The Deputy, which vilified the pope, accusing him of silence and inaction over the Jews. It was a trend that intensified with the publication of Hitler's Pope, a book by John Cornwell.

However, as the Vatican's secretary of state before the war, the future pope contributed to the damning 1937 encyclical of Pius XI, With Burning Anxiety, and, as Pius XII he made condemnatory speeches that were widely interpreted at the time – including by Jewish leaders and newspapers – as clear condemnations of Hitler's racial policies. Due to the Vatican's traditionallydiplomatic language, the accusation that Pius XII did not speak out has festered.

Professor Ronald J Rychlak, the author of Hitler, the War and the Pope, said: "Gordon Thomas has found primary sources … He has tracked down family members, original documentation and established what really was a universal perception prior to the 1960s. He's shown what the people at the time – victims, rescuers and villains – all knew: that Pius XII was a great supporter of the victims of the Holocaust."

Asked why the Vatican had not made the new material available until now or, where stories were known, disseminated them more widely,Thomas said: "The church thinks across centuries. If there's a dispute for 50 years, so what?"

William Doino, a Vatican historian, described Thomas's research as "unique and