French television can be the dullest in the world – but justice where justice is due. Jean-François Delassus has just sent me his 100-minute documentary for France 2 on the 1914-18 war – 14-18, Le Bruit and La Fureur – and it is an absolute cracker.

Not only has the archive footage been brilliantly "sounded" (the French sonorisé is somehow more elegant) but it has been expertly colourised. French troops march to their deaths with red kepis; British soldiers celebrate the end of war in brown uniforms (along with a Brit who has dressed himself up in German field grey plus rifle and bayonet).

At one point, an airship, movie camera attached, flies over the mud of the trenches and across a smashed French town where streams of refugees are trudging home. Some of this is so startling that it's difficult to realise that everyone in camera-shot is long dead.

Not all of the footage is new. The British film of the Somme contains some familiar carnage but the French battle of Chemin des Dames is absolutely terrifying. At the Somme, General Haig had a plan that didn't work. At Chemins des Dames, Nivelle didn't even have a plan and the French mutinied. They wouldn't abandon their trenches and go home – the great fear of every Allied general – but they wouldn't go forward (an eminently sensible idea) until Nivelle was fired and replaced by our old chum General Pétain. And there they all are – in full colour.

Some elements of this extraordinary film I took exception to. I'm not sure, for example, whether the use of movie film clips, albeit scrupulously labelled, in among the archive material really works. But the music, specially composed for the film, has a brooding orchestral majesty. It's almost impossible not to cry. There is one haunting shot of a French peasant soldier, staring into the camera and suddenly breaking into an innocent smile.

Far more terrifying is the footage of war wounded, heads half torn away, ears missing, jaws missing. A shell-shocked soldier is marched into the square of a military hospital and half-walks, half-staggers, head to the ground like a broken animal before a doctor (in a vilely dirty jacket) pats him on the back and he leaves.

At the top of a shell-snapped tree, a soldier lies on his back, head down, his corpse spiked through with wood, crucified by gunfire. And my God, the guns do fire. British guns, German guns, French guns, even Italian guns, spitting rocks off snow-covered mountainsides. Even the Versailles palace comes alive in gold. At the 1919 treaty, one elderly French statesman said that Europe had won itself a 20-year ceasefire – he got it spot on.

How did men survive in this hell, the film asks us, and I am not sure the question is answered. I suppose there is a camaraderie in war although I have yet to witness it. (There is a very funny but dark shot of a trench of British soldiers getting snowballed by their comrades.)

But then again, every soldier believed he would be home by Christmas, and then by the Christmas after that and then by the next Christmas. And I rather suspect that's what happens in wars. There is always going to be one more push, one more brilliant attack, the great break-out. And when wars end, the exhaustion has drained the energy out the populations that have fought.

But this is not just a war film. Before 1914, we actually see the crowds of Paris taking their café au lait in brightly coloured hats. An old green French metro train glides self-confidently into a station as the entire world – the belle époque of one soldier's memory – drifts grotesquely towards that awful war.

I hadn't quite realised how much combat footage exists from 1914-18, but when Delassus' film ends, there is one quite awful moment.

From right of the camera a squadron of British cavalry rides in line across open countryside on the Western Front. I watched mesmerised. Why were we watching this after the final captions? And right in the middle of the line of riders, a shell suddenly cracks down and you can just see two horses writhing in agony.

One horseman gallops back towards the devastation. And then, from close to the left of the camera, a British soldier, holding his helmet on to his head, runs across the countryside to the smoke and carnage. And just as he is about to reach it, the film runs out.

We don't know where this happened; we do not know the British regiment or its casualties, just that lonely figure running under fire to help his mates. A soldier of the Great War.