There is of course a mountain of evidence to support the fact that the Nazis murdered upwards of six million Jews during the Second World War.

However, there are still people who deny the Holocaust, which is pretty much akin to people denying the existence of the Pacific Ocean.

Of course the thing to do with Pacific Ocean deniers is to fly them out to Los Angeles and take them down to Venice Beach for a look. It is a little more complicated with the Holocaust. For example, deniers have often claimed that the Treblinka death camp in Poland was used merely for transit and that no Jews died there. If you go there now, as Jonathan Charles did for the making of this penetrating documentary, you will see very little but for a watchtower and some ramshackle fencing in a forest clearing – the Nazis systematically destroyed the camp in their retreat from the Soviets.

Moreover, because the only industry which took place in the camp was that of murder (some 800,000 were killed in this one camp – the equivalent of the entire population of Glasgow plus surrounding towns), there were only 70 survivors and most of these are now dead.

But you do not have to scratch far beneath the surface to find the evidence for slaughter on an unimaginable scale. In fact, as Caroline Sturdy Colls of the University of Birmingham discovered, above the mass burial pits where the corpses of hundreds of thousands were buried, the soil quality is so poor that practically nothing has taken root there in nearly 70 years.

Sturdy Colls and her team wanted to find more conclusive evidence of where the mass graves were located. Because Jewish law forbids the digging up of the ground, Sturdy Colls and her team used new technology – ground-penetrating radar, sending pulses into the earth which are reflected from buried remains. She believes she has now located the pits – some of them vast.

One does not need too much of an imagination to visualise the scenes of utter horror which must have been repeated on a daily basis at the camp. But just in case, Charles used the testimony of survivors, including Kalman Taigman, who remembered arriving at the camp and being hit on the head as he was being separated from his mother, and never seeing her again.

The memoirs of another survivor, Chil Rajchman, relate how the embers from the ovens settled over a pit containing some 250,000 bodies and set the whole area alight – the rotting corpses of a quarter of a million Jews fuelling a grotesque bonfire.

The deniers will be able to go over and examine the evidence for themselves now. One presumes that very few will make the trip.