Rodents: Mice!!

What's the best way to get rid of mice? No poisoning though. I don't know where they are coming from, I'm on the 1st floor and I am extremely clean. Like I'm not even untidy. This is driving me crazy. When my SO leaves they harass me! I live in London so this is something Normal I guess.
Do you know any cunning tricks to kill them quickly? Omgg.. that sounds so evil! But that's how I feel, they don't pay rent here, I do!