Revealed: the hidden Nazi death camps

Their research corresponds to a death toll of six million Jews but Dr Megargee said it suggested that up to 20 million — Jews and non-Jews — went though the system, even if not all were murdered.

It is not possible for people to say they did not know what was going on in the Shoah

The newly-collated evidence has been hailed by campaigners against Holocaust denial. American historian Professor Deborah Lipstadt, who won a libel battle in 2000 with Holocaust denier David Irving, said it was “exceptionally important”.

“Just when we thought we know it all — we don’t”. She hoped that deniers “would be forced to confront this evidence. It makes it impossible for people to say they didn’t know what was going on.”

Germany has accepted the new research as evidence that can be used in court cases.

The details reveal how, across Germany and occupied areas from North Africa to Norway, the Nazis built camps. The researchers document 980 concentration camps and 1,150 Jewish ghettos.

Some are sites that “nobody knew about at all”, but Dr Megargee said the discrepancy was also because historians had tended to focus on “particular camps or particular kinds of camps… nobody had pulled it all together.

“An awful lot of sources only became available when the Iron Curtain fell. Beyond that, there are records on the Nazi camps system scattered throughout a dozen different countries in as many different languages,” he said.

Survivors say they are not surprised. Vienna-born Freddie Knoller, 91, said: “I have spoken to other survivors and they have mentioned a lot of different camps that I didn’t know about and have never heard of before — especially from east Poland.”

Frankfurt-born Henry Wermuth, 89, survived at least eight camps, including periods at Kraków-Płaszów, Auschwitz and Mauthausen. He said that in addition to the well-known camps, “there were many small camps run by the SS and army.”

Alec Ward, born Abram Warszaw in Poland, spent time at two ghettos, three slave labour camps and two concentration camps. The 86-year-old said: “The findings don’t surprise me. A lot was done in secret by the Germans to annihilate as many Jews as possible.”

All survivors are members of Jewish Care's Holocaust Survivors' Centre in Hendon.

Dr David Silberklang, senior historian at Yad Vashem in Jerusalem, said: “This is an important piece of research. What they’ve come up with has been fantastic. They’ve looked at a wide range of sources, used experts and explored different kinds of camps — and they’re still in the process of publishing their findings.

“There’s a lot more out there that we don’t know about. Yad Vashem has found more Jewish communities across Europe than we initially knew about. We’ve also found around 1500 killing sites in the Yad Vashem-led Killing Sites Project — and that’s only looking at the Ukraine and Belarus.”

But the Washington research was dismissed by Dr Efraim Zuroff, director of the Israel office of the Simon Wiesenthal Centre. He said his initial reaction was “one of annoying dismay” and complained about a “PR blitz” and “sensationalism”.

He said: “For decades it has been obvious to historians that the number of Nazi camps, ghettos, and other places of persecution was astronomical and historically unprecedented”.