Meanwhile, in the Westhoek of West Flanders - scene of some of the most severe battles of the First World War - the locals must have been wondering what all the fuss was about, because such discoveries in their region are far from newsworthy.

Members of the local bomb disposal squad might have been caught smiling ruefully, too. In 2009, they were called out no fewer than 3,027 times - that's more than eight times a day - to pick up unexploded ordnance from the First World War. These call-outs resulted in the disposal of 215 tons of unexploded bombs, shells, mortars, grenades and gas canisters.

Yet the timing of the discovery of the NATO bomb couldn't have been more apposite. Only five days previously, the 11 November lecture of the Flemish Peace Institute was held in Saint Jacob's Church in Ypres. This annual event is jointly organised with the In Flanders Fields Museum.

The keynote speech this year was delivered by Flemish author Erwin Mortier. His prize-winning 2008 novel Godenslaap (Sleeping Gods) was reviewed in the Frankfurter Allgemeine Zeitung: "This book depicts daily life during the First World War in such an impressive way that it seems as if Mortier has experienced the war himself."

In some respects, he had. When he was eight, he was playing toy soldiers with a friend on local waste ground; the game involved excavating mini- trenches and tunnels. "As we were digging deep inside a mound of earth, our fingers came across something hard and domed which felt granular and gave a dull metallic sound when we knocked on it."

The two boys forgot about their game and started digging for buried treasure. Eventually they pulled out two soldier's helmets, rust-coloured through corrosion, one with a perfectly round hole in it. The boys took their finds to Mortier's father, who promptly forbade them to play in the heap of earth: "He said we were lucky, not because of our treasure trove but because our fingers had encountered a couple of helmets, and not anything far worse than that," Mortier recalls.

Discoveries in the Flemish soil that could be "far worse" were also touched on by Luc Dehaene, mayor of Ypres, at the 11 November lecture. He spoke of someone who was not so fortunate as Mortier and his friend.

Civil victim, 90 years later
Maité Roël was also eight years old when, on 6 July 1992, she was sitting with her friends around a campfire of the naval scouts in the military zone in Wetteren. There was an explosion, and everyone started shouting and running around. But Maité couldn't get up. She looked down and saw that her left leg was hanging by a piece of skin.

The screaming child was rushed by air to Ghent University Hospital. Surgeons took skin, muscles and arteries from her thighs, back and ribs to reconstruct her leg. Eventually, after 29 operations that involved Maité spending two years in hospital, heavily sedated on morphine, surgeons managed to save her leg. Today she is recognised as a civil victim of the First World War. She even holds a First World War veteran's card ("mutilated in the war"), and when she shows it to gain reduced fare on the railway, ticket inspectors suspect she's stolen it from a dead ancestor.

It appears that one of the scouts had picked up an unexploded shell, thinking it was a mouldy log, and tossed it into the fire. Studying the shrapnel revealed it was an RAF bomb, dropped on the fleeing Germans in 1918. Ironically, Maité is partly British; her grandmother is a Scot who lives in Ostend.

Unfortunately, Maité's story is far from unique. Children playing in Flanders fields, or even in their gardens, frequently unearth war-time relics. Some, like Erwin Mortier, are lucky. They find harmless items such as coins, buckles, cutlery, buttons, belts and gasmask filters. Others, like Maité Roël, find items much more dangerous, sometimes with horrific consequences.

"In the district of Ypres, 599 people have died as a result of deadly ammunition that was left behind after the Armistice," says Dehaene. "The last victim died just two years ago, and nobody dares to say that this is finally the end."

The iron harvest
Local farmers also plough out unexploded shells every season. It's known as "The Iron Harvest". The source is the approximately 720 million shells and mortars that were fired on the western front between 1914 and 1918. Their reliability was so poor that it is estimated that at least a quarter of them did not explode at the time.

Many were recovered after the war, but experts estimate there may still be as many as 30 million shells lying in the earth along the front line. One in 20 contains poisonous gases that are still potent enough to kill.

Each year at least 3,000 shells turn up in the Westhoek; there are so many that the annual haul is measured in tonnage rather than projectiles. And, with farmers using heavier equipment and digging deeper, there is no sign of the figures decreasing.

Worryingly - and amazingly after nearly a century - it's a race against time. The years of corrosion have left the old shells with ever thinner, more leak-prone casings. When handled, gas canisters can more easily disintegrate and release their loads of mustard gas, phosgene or phosphor into the ground, or over their unlucky handlers.

The Explosive Ordnance Disposal Service (DOVO) retrieves ordnance each day from the Westhoek, where four of the First World War's great battles were fought. Sometimes the team makes several stops a day, often finding a pile of shells stacked up outside a farm's gates, like refuse left out for the garbage collector.

Bigger, single finds are also common. In 2006, near Brugelette, 450 kg of artillery and mortar rounds were discovered in a German ammunition bunker. And just last week, on 22 November, an entire village, further along the front line in northern France, was evacuated for a week while a team of bomb disposal experts cleared 30 tons of shells from a First World War German munitions depot. The depot measured 16 x 1.5 meters and was discovered one meter below ground by a villager while gardening.

Piling munitions in Poelkapelle
But what happens to this Iron Harvest? In West Flanders, the daily haul is trucked to the DOVO base in Poelkapelle, about 10 kilometres northeast of Ypres. Here, the shells are gingerly sorted by calibre and nationality. Until late 1980, projectiles identified as containing poison were dumped into the ocean off the coast of Belgium. Since then, they have been stacked on top of each other in readiness for being dismantled.

Dismantling is a slow, labour-intensive process. Only 20 gas canisters can be handled each day; the current stockpile stands at about 20,000, which means plenty of dangerous work for years to come. To aid this work, the Poelkapelle unit now has two large X-ray machines, capable of detecting if a shell is filled with poison, and a neutron-induced gamma spectroscope, for identifying which type of toxin.

The rest of their haul - varying in size from a can of Coca-Cola to a kitchen refuse bin - is placed in wooden crates, wired to a fuse and loaded into a deep hole in the ground. Every day, the holes are covered with earth, a warning siren sounds, a button is pressed, and the fields of Flanders once more resonate to the chilling sound of shellfire.