A former SS guard who became known as the Bookkeeper of Auschwitz is challenging his four-year prison sentence because it violates his “right to life”.

Now 96, Oskar Groening was convicted in 2015 of being an accessory to the murders of 300,000 people at the notorious death camp.

His trial heard that he was a Nazi accountant who sorted and counted the money taken from those killed or used as slave labour, and shipped it back to Berlin.

On a number of occasions he was also assigned to “ramp duty”, which involved processing deportees they arrived by rail in cattle cars.

But despite his conviction more than two years ago, Groening has been living at home and has now mounted an appeal against his imprisonment.

Last month a court ruled that he was fit to serve his sentence, but his defence team has taken the matter to Germany's Constitutional Court, claiming prison would amount to a violation of his basic rights at such an advanced age.

His lawyer Hans Holtermann told the DPA news agency: “In terms of constitutional law, it should be examined if the health condition of Mr Groening allows for his basic right to life and physical integrity to be guaranteed."

Groening was subject to several lengthy probes dating back to the 1970s and ultimately cleared of wrongdoing.

But a case was reopened against him in 2011, when the legal basis for prosecuting former Nazis changed with the landmark conviction of John Demjanjuk, a guard at the Sobibór extermination camp.

Fewer than 50 of the 6,500 SS personnel who were stationed at Auschwitz and survived the war were ever convicted for the atrocities they committed there.