There are more than enough duds from World War II. In the Ruhr area alone, around 5,000 larger bombs are suspected. Every year one hears/reads about about 20 finds. A few years ago, half a residential street in Munich was reduced to rubble while trying to defuse a large bomb.
In western France, Luxembourg and Belgium (especially in the Ardennes) some are also found again and again.
I don't know how things are in the UK at the moment, in Germany duds are already the norm.
Greetings
Ray
Be human, stay human
When flying, the dangerous thing is the earth (Wilbur Wright)