The truth about the million British horses that served in World War I is even more epic than Steven Spielberg's War Horse feature film.

This documentary tells their extraordinary, moving story, begining with the mass call-up of horses from every farm and country estate in the land. Racing commentator Brough Scott tells the tale of his aristocratic grandfather General Jack Seely and his beloved horse Warrior, who would become the most famous horse of the war.

The British Army hoped its illustrious cavalry regiments would win a swift victory, but it would be years before they enjoyed their moment of glory. Instead, in a new era of mechanised trench warfare, the heavy horses transporting guns, ammunition and food to the front-line troops were most important.

A quarter of a million of these horses died from shrapnel wounds and disease. But the deep bond that developed between man and horse helped both survive the hell of the Somme and Passchendaele.

Behind the lines an army of vets worked miracles to treat injured horses and keep them going. The finest hour of the cavalry came in spring 1918 when - led by the warhorse Warrior - they checked the German advance before going on to help win the war.

But there was further heartache when the war ended. Eighty five thousand of the oldest horses were sold for meat to feed POWs and the half-starved local population.

Half a million horses were sold to French farmers to help rebuild the countryside. Only 60,000 made it back to Britain.

Six of these horses would pull the body of the Unknown Warrior to its last resting place in Westminster Abbey.