Well based on media discussion of a current major UK story - that 39 immigrants died in a refrigerated lorry, it's spawned a lot of stories into illegal immigration and
why 39 people were trying to get to the UK. Police are currently investigating the lorry having been one of a convoy of three - so potentially around 100. One of the reports, that I can't find again, I think someone at Rotterdam port discussing that some unbelievably low percentage of trucks are checked properly in the major EU ports, and few even have capability to check for presence of people. Just a check that seals are intact, papers are right, and a camera to see passing vehicles.
So it's probable that many Europeans could have encountered illegal immigrants without realising.
The common point is there a selection of low pay service jobs that attract illegal immigrants, who then become trapped. Some by debt and threats to family, and other more direct slavery. Anti-trafficking and similar groups have been warning of issues for years, and mostly ignored.
It remains a truth that the vast majority of immigration in Europe is legal, but there is a significant level of illegal migration. Thanks to the free movement of peoples within the EU, it is far harder to detect than before those border checks were pulled down.
Here is just one of a selection of pieces that have come up this week across all the press:
https://www.theguardian.com/law/2019/oct/25/trafficked-vietn...