So they marched, north away from Pevensey. Their first objective was five miles or so inland, a place named on the leutnant's map as Windmill Hill. They soon left behind the rather dilapidated seaside villas at Pevensey. The column followed minor roads and farm tracks, but made reasonable progress over the level salt marshes beyond. The day stayed grey, even as the light gathered, and the drizzle and mist was depressing. 'If this is England, Churchill can keep it,' one man murmured.

But as Ernst walked with his comrades, swinging his arms and stepping out, he felt his blood flow, his heart pump, the clean English air filling his lungs, and he began to feel alive again. Why not? He was young, he was strong, his training was good, and he was with the best army in the world, a fact proven by accomplishment. He dared to look ahead, to the future. Perhaps he would be in London when the Fuhrer made his entrance – by barge, perhaps, along the Thames. What a grand day that would be!

The men rumbled into a marching song – 'Bomben auf Engelland', a popular favourite on the French beaches.

But this mood did not last long. Aircraft buzzed across the sky, out of sight above the lid of low cloud. Ernst winced every time one came close; he had seen troop columns strafed from the air on the continent. But no harm came from that quarter. Rumours went around the column that the RAF today was targeting the embarkation ports in France and the returning fleets of barges and tugs, trying to disrupt the invasion's second echelon.

And as the morning wore on the going became slow, disjointed. The first serious resistance they encountered was at a crossroads near a pub called the Lamb Inn, a location that commanded the levels behind them. That didn't take long to resolve, thanks to the tank. But after that the resistance became more frequent, and over and over again the column ground to a halt. Often Ernst couldn't even see what was going on up ahead. He would hear the thump of explosions, the pop of small-arms fire, occasionally a roar as the tank let loose its main gun, and see the smoke of burning petrol. Sometimes they would see one or more of their own vehicles, disabled or burned out and shoved over to the side of the road. There were a few German dead, a steady trickle; Ernst saw the bodies at the side of the road covered by tarpaulins from the disabled trucks. Medics patched up the injured.

And the troops would stare as they passed a blown-apart pillbox of piled-up sandbags, or a cleared-aside roadblock made of concrete and lengths of rail track and concrete anti-tank 'dimples', lines of little cones. The weapons in the blown-open pillboxes and bunkers, seemed crude. Ernst saw one mortar that looked as if it might have been used against Napoleon.

On they went. Every bridge was demolished, and the scouts had to find them places to ford the streams. Elsewhere there were ditches, meant to stop tanks perhaps, and the weary men scrambled down one bank and up another. These assaults were petty, but they steadily eroded the column's manpower, and took out their vehicles and horses and used up their ammunition. And, more importantly, they were slowed down.

A horse was killed by a mine in a grotesque explosion that burst the animal's carcass, showering the men with bloody fur and shredded bits of meat. The men took a break as the engineers dealt with that.

Two British troops, wounded but alive, had been taken in this place. The men sat on the ground with their hands on their heads. They wore what looked like proper army uniforms, with flat steel helmets, leather gaiters, boots, greatcoats and leather belts. One had an officer's stripes. But their arm bands read HOME GUARD. These two were old, Ernst saw with a shock as he passed, their hair grey, their faces deeply lined – either of them old enough to be his own father, if not his grandfather. Perhaps the rumours that had been circulating since France were true, that the British forces really were badly depleted by the catastrophe that had overtaken them at Dunkirk. Old these fellows might be, and defeated and captured, but they sat up straight like soldiers, one with blood trickling into a closed eye from a head wound, and they stared every German in the eye.

'Partisans?' muttered one man.

'No,' the leutnant snapped. 'You can't be a partisan until your country has surrendered, Breitling. Until then these gentleman are to be treated as prisoners of war.'

'They should be fucking shot,' Breitling said. 'Fucking English. Why can't they just roll over like the French?'

'Don't let it get you down, lads,' said the leutnant. 'Look at what we're up against. Old men and boys, and weapons from a museum. When the Panzers get over here on Tuesday they'll roll up this countryside like a carpet.'

But later Ernst overheard the leutnant muttering with an officer about this slow progress, and how it was becoming important they found fuel before they exhausted the supply they had brought over from France.

For Ben and the other prisoners it was not an arduous walk. Stuck in the middle of the column and surrounded by guards, they plodded steadily along. They talked quietly, swapped their stories, and bummed furtive cigarettes from each other. They seemed resigned to their fate, Ben thought.

The prisoners had to shelter like the rest from the attacks by the resistance elements. This was another product of the war in Spain, Ben supposed, that great warm-up fixture where the Germans had learned how to machine-gun civilians from the air and the British had learned to make Molotov cocktails.

As the day wore on Ben's headache got worse.

One man helped him when he staggered. 'Just walk. It was like this in France, in the early days. March and march. You just have to get on with it. My advice is to think about something else.' He had a strong accent, barely comprehensible to Ben. 'You got a girl?'

'Not exactly.'

'Well, you're a bright lad. Do a crossword in your head. That's my advice.'

So Ben walked, trying to ignore the pain in his head. He tried to visualise problems in relativity, like Godel's beautiful rotating-universe solution of Einstein's equations. But the math kept sliding away from him, the tensors with their forests of suffices blurring into invisibility.

Soon he had trouble keeping up with the pace, and drifted to the back of the little group of prisoners. The German guards thumped him with their rifle-butts, yelling at him to keep up, and even rode into the back of his legs with their bicycle wheels.

The veteran protested: 'Hey, go easy, Funf. Can't you see he's ill?' That won him shouts in German that if he didn't shut up he'd be taken out of the line and shot. The veteran understood their tone, if not their words. 'The front-line corps who captured us were gentlemen. Not like this shower. Look at them, car mechanics and horse handlers, bottle washers and sausage makers. Scum of the earth, the lot of them.'