Jack Fairweather’s biography of the Polish resistance fighter who infiltrated Auschwitz to report on what was taking place there has won the Costa Book of the Year prize.

The Volunteer, hailed by chair of judges Sian Williams as “a book that needs to be read”, tells the story of how Polish resistance fighter Witold Pilecki assumed a false name to be captured and taken to the death camp, in order to bear witness to what happened.

He survived in the camp for two years, smuggling reports out, before escaping and rejoining the Polish resistance.

After the war, he was executed by the Polish Communists as an enemy of the state.

Mr Fairweather, a British war reporter who has worked in Afghanistan and Iraq, took immense pains in accurately recounting the story. spending for more than three years, with a team of Polish and German translators to get it right.

Ms Williams said the book was “an incredible story; pacy like a thriller, it reads like fiction and yet it’s not, it is fact.”

When Mr Fairweather spoke about the book to the JC last July, he said: “I knew it was a great story.

“I wanted to show in the book how information about Auschwitz as an extermination centre reached the West much sooner than had previously been thought.”