what will happen is, police will come, you are in your house, some idiot claims to have legal right to the house, he cannot present SHIT, and at worst he will file some police report about you throwing him out, of which you might be fined.
That’s silly. You have scope out the place with your friends, and then wait till they leave for the weekend somewhere then break in and change the locks.
He might be hauled away if you manage to provoke him to hurt you, or cut your electricity, water. There is this idea that the squatters are all ignorant people. A lot are quite well educated on the legal aspects of the operation, have accomplices, and know exactly what to say and act when confronted.
Does the law specifically say that breaking in is allowed by anyone except the legitimate owner?
My mom's husband had rented his previous flat (to complement his pension) to two women. They were working, very "normal" persons, and the contract specified that no other person could live there. One of them started dating a man and, a year later, there were three, then four (a child) living there. Then the other woman left (the guy was violent) and then the mother and her child had to flee too.
So my mom's husband had a guy that he never had any agreement with, living in his property, not paying rent, and not paying utilities. Now the law forbids to cut the utilities so you have to pay utilities for him. I think at the time (five years ago) it was still possible to cut. But the guy didn't care. After a year and a hell in courts, the flat was free again but a complete mess, broken furniture, mountains of junk. To weeks were needed just to clean, then paint, fixing doors, plumbing, etc.
He sold it ASAP. Now, I don't wonder why there's so little housing for rent.