Just curious, back in the 80’s I seem to recall hearing that in England, if you left your apartment for any length of time, you ran the risk of someone moving in, changing the locks, and asssuming residency, & that somehow this was legal & not that uncommon. Any truth to that, or just a bit of fun foisted on the latest drunk american kid by the locals down at the Rose & Thistle, the Slap & Tickle, Goat & Pickle or wherever the hell I was? Thanks for any info 
Sort of true for England but not that simple - adverse possession requires a long period of continuous occupation. See the UK section of the wiki articleon squatting - obviously written by someone in favour of squatters but covers the ground reasonably well.
Dunno about the UK, but in the Netherlands, it’s (as of yet) still (sort of) true*. Plans are underway to criminalize it, though.
- Basically, a residence has to be unoccupied for some period (IIRC something like 1 or 3 years) and then squatted for a (shorter) period, meaning people will have to really live there for some time. After that, the occupants basically get renter’s rights, meaning the owner can’t kick you out without a whole lot of legal issues (or illegal - read: violent - actions, which also happens).
The mechanism was sort of legalized in the early 80s when housing was very hard to get in the major cities but there also were a lot of empty residences and other buildings by owners who basically were waiting for the economy to get better (so they weren’t renting or selling, just holding on to the - empty - property, some times for decades).
Too late to add: many of the shops in the inner center of Amsterdam have 3 to 4 stories above them and many of those were just closed off to make a bit more space for the shops on the ground floor (shopping space being far more profitable to rent). Quite a lot of those got squatted too.