In fact, after the war, the red zones were quite extensive, but there was an intense lobbying to reopen these lands to agriculture.
In the 20ies, a farmer detonated an unexploded ammunition was not an uncommon occurrence.
Nowadays, this is a really rare event, I think there was a case in Belgium about 10 years ago, but it's quite uncommon.
However, when you dig, you always find something. My mother started a small garden (about 4 x 8 meters) a few years ago and when she worked the soil for the first time, she found various leftovers like shell heads, shell fragments, bullets, lead spheres used in shrapnel rounds, etc.
And it's not uncommon to find unexploded shells on the side of the roads, farmers when they find them, put them on the side of their fields.
When my mother was a child in the 50ies and 60ies, she used to help her parents collect these various metal fragments as it was a way to get a small additional revenue for the family. When we cleaned-up my late grand-father's house, there were buckets full of those in fact. There was also an unpinned unexploded grenade by the way. If I recall correctly, they called the local "garde champetre" to deal with it, and it's still in his attributions to deal with such finds.
However, there are some big ammunition depots in north of France with all these WWI shells collected over the years. And a lot of those shells are still not neutralized.
Also, another interesting side effect is all the cemeteries in the area, the land is literally peppered with them.
And these cemeteries are UK territories (In fact the Thiepval monument is one of the highest structure on UK soil and in continental Europe). This was actually a blocker for a nearby city (Albert) when they tried to extend their airport, they were blocked by these cemeteries.
This seems to be something that some British tourists like to do. At Paris Gare du Nord where you board the Eurostar train to London there are signs saying that you are not allowed to bring explosives that you dug up as souvenirs on board a fricking train.
> In fact the Thiepval monument is one of the highest structure on UK soil and in continental Europe
What do you mean? Highest in what sense? According to Wikipedia it's 43 meters high, which isn't a lot, so that cannot be what you mean.
As for the Thiepval monument, I meant one of the tallest building on sovereign UK soil, but outside the British Isles. However, I've heard in a casual conversation, I'm not sure it's actually true. Yet, it's definitely a big memorial monument ^^, you can see it from miles away.
(Though, off-topically, I don't necessarily buy the "UK soil" part. Supposedly even the "embassies are foreign soil" thing is more of an urban legend than legal reality. Also, the monument being the property of the UK should be enough to block its destruction.)
It depends on what you mean by "foreign soil." Embassies are extraterritorial--as the name implies, it does not represent a claim on land, but the laws of the diplomat's country, not the host country, generally apply. This difference is sometimes crucial: being born in an embassy would not give you jus soli citizenship and GWB set up the terrorist prison in Guantanamo Bay to try to ensure that the Constitution wouldn't apply (since Guantanamo Bay isn't US soil, it's a base leased to the US by Cuba).
Yes, it might be a little more complex than that:
> On 29 December 1915, a law was passed creating a right to a perpetual resting place on French soil to any soldier in the French army or Allied army who had died for France. The land that contains the UK's war cemeteries abroad is held "in perpetuity" by the Commonwealth War Graves Commission (CWGC)
Every time they dig to start a new building, they find some exploded bombs. And each time, it's an evacuation of a lot of people in the city center to deal with it (easily a few hundred meters which in a city center means a few thousands people).
However, leftover bombs from WWII are a bit different. They tend to be bigger, hundreds of kilograms where the "typical" shell you find in old WWI battlefields are less than 10 kilograms. Also the problematic is a little different since on one side, it's a medium to big city, on the other it's mostly the countryside.
Birmingham is the same. There was a WWII bomb found last year right by two major roads where they cross a railway line. Travel into the city centre was completely stuffed up for two days. I felt the controlled explosion three miles away.
Normal shells are fairly easy to dispose of using explosives, so those might be poison gas shells. I know Belgium had an enormous backlog in destroying such shells in Houthulst even as recent as 15 years ago (http://www.greatwar.nl/frames/default-houthulstn.html), but don’t know what happened with it (at the time, there were talks on the urgency of cleaning it up)