Brexit was the best experiment for that. They kick immigrants out so all jobs went to the local population. People didn’t want them, produce was left in the fields, deliveries were not made, tables were not waited on and some companies folded. Anyway, immigration is now back and higher than it used to be, but from other countries.
Wait, so they got rid of the Poles and other Eastern Europeans they loved to hate—who are they importing for labor now?