There are two other men alive who served between 1914 and 1918, but neither experienced the living nightmare of the front line. Henry Allingham, born two years earlier than Mr Patch, served in France with the Royal Naval Air Service and occasionally visited the front to recover downed aircraft, while Bill Stone was called up for the Royal Navy only two months before the Armistice and did not see action.

Mr Patch takes no pride in being the last of the millions who fought and died amid unmitigated horror. His improbable status sometimes overwhelms him, reducing him to silent contemplation.

"The poor bloody infantry. Dead right. That's what we were. For 1/6d a day."

His speech is slow and deliberate; gentle, rusty Somerset. Kaiser is pronounced "Kay-zer", with a long "z".

That he is sitting here, listening to children in a nearby playground, is a testament to life's caprice. He should have died 90 years ago, on a black night in September 1917, with his mates. It would have been an unremarkable death: one more shredded body to add to three others.

He was part of a Lewis Gun team in the Duke of Cornwall's Light Infantry, a close-knit family drawn closer together by the knowledge that machine-gunners, by virtue of the mayhem they wrought among advancing infantry, were likely to receive no mercy if over-run.

That night, his battalion had been pulled out of the line and was moving to the rear over open ground when a German shell, a "whizz-bang", exploded. The young Private Patch was wounded in the groin by a shell splinter. One other member of the five-strong team survived. The others were blown to pieces.

"It killed Number Three - he came from Truro - and Number Four and Number Five. Jack and Jill we called those two. They came from Falmouth. Number Three was known as Maudy. There was an actress of that name. He had a good sense of humour."

Were they good friends? "All of us."

Did they look after each other? "Always."

The British Empire suffered 500,000 dead and wounded during the three months of Third Ypres, as Passchendaele is more properly known. The offensive was the brainchild of the British commander-in-chief, Field Marshal Sir Douglas Haig, and didn't take long to bog down in the morass created by incessant artillery bombardment and constant rain. Casualties mounted.

Between the start of the campaign on July 31 and its end on November 8, an average of 5,000 men a day were killed or wounded, and all for the capture of a few miles of desecrated land.

Harry Patch grew up in Coombe Down, near Bath. He left school at 15 and trained as a plumber. He was 16 when war broke out and reached 18 just as conscription was being introduced. Unlike many of the young men who smilingly signed up for death and dismemberment, he had no illusions.

"I knew what to expect. My mother had three sons. My oldest brother suffered from asthma. He didn't pass. My middle brother was a regular soldier. Royal Engineers. Serving in Africa. He was called home and wounded at Mons. I knew what it was going to be like: dirty, filthy, insanitary."

It met his expectations. There were the lice that clung to the body and the rats that gnawed fearlessly at bootlaces. And the mud. Thick brown liquid quite capable of drowning a man. The shell burst that killed his friends ended Mr Patch's three or so months in the front line.

"I can remember the shell bursting. I saw the flash, I must have passed out. The next thing I could remember was the dressing station. A wound in my groin. The nurse painted something around it to stop the lice getting at it. I was given a good hot bath. The lice came off - you could pick them up with a shovel - bloody things."

There was a shortage of anaesthetic and he had to be held down as the shell splinter was removed. The medical officer asked him if wanted to keep it as a souvenir. Mr Patch told him what he could do with it. "The fella in the next bed said to me, 'If he writes anything in that book, you're for Blighty.' Well, he did write in the book. I didn't believe it until someone came in and called my name and number. I went to Rouen."

During his recovery in Britain, he met his first wife. "Knocked her down. She was coming down some steps from the cinema and I was running for the bus and knocked her down. Picked her up, dusted her off and it started from that." They were married for 56 years and had two sons, both of whom have since died.

Mr Patch has few mementos from the war. He was too old to fight in the Second World War and worked as a sanitary engineer in American army camps in the south-west. He retired in 1963. Following his first wife's death in 1976, he married again at the age of 81. His second wife died five years ago.

His membership of that steadily diminishing band of British veterans of the war to end all wars has earned him audiences with the Queen and the French Légion d'honneur. A few years ago he was taken to meet a German veteran who had fought opposite him in Flanders. "Nice old chap. A pacifist. Same as me. Why did they suffer, those millions of men?"

The afternoon is wearing on and Mr Patch is tired. He pauses to listen to the children playing. What does it feel like to be the last of those millions, that army of ghosts?

"I don't like it," he says and then adds: "I sit there and think. And some nights I dream - of that first battle. I can't forget it.

"I fell in a trench. There was a fella there. He must have been about our age. He was ripped shoulder to waist with shrapnel. I held his hand for the last 60 seconds of his life. He only said one word: 'Mother'. I didn't see her, but she was there. No doubt about it. He passed from this life into the next, and it felt as if I was in God's presence.

"I've never got over it. You never forget it. Never."