Passport confiscation is a common sign of modern slavery.
"he was lured in with the false promise of a well-paid job in the UK"
"The gang confiscated the passports of all their victims"
It's not legal. There are definitions of "Modern Slavery" and descriptions of the practices and warning signs because it is still an issue in contemporary times, including in Europe.
No, it's real. Every year, there are several news articles about berry pickers being abused, at least here in Sweden (not sure about the other Scandinavian countries). Here's [0] just ONE of the myriad of articles I could find, but there are so, so, so many more (and even worse ones) [1].
Similar situation in Finland. There have only recently been some consequences for the berry companies and reforms are underway. The pickers would come mainly from Thailand with tourist visas. This year a majority of the visas have been denied and the berry companies are throwing tantrums.
They've been engaging in illegal price-fixing, too.
https://www.bbc.co.uk/news/articles/c2kdg84zj4wo