Genuine question: Do you think that people in countries with strong labour laws are signing up to be literal slaves?
So yes, sometimes strong labor laws have a hint of slavery to them, but certainly not equivalence to real slavery.
Most UK contracts will also include a clause allowing the company to end the employment immediately as long as they still pay out what the employee would have earned during their notice period.
Having been through a few roles in the uk myself, the obligation on the company to give me adequate notice (and pay) has always benefited me.