Squat or not??

Hi,

If a person is living in my property, without having signed a tenancy agreement, and they no longer have permission to be staying in the property, does this class them as a squatter?

Naively, I initially allowed the person to move into the property prior to them signing the tenancy agreement. They have since been un-cooperative and have yet to sign the contract, nor pay me any rent.

Under what circumstances can I evict the "tenant". If they're not under contract, is it a criminal offence for them to be living in the property if they no longer have my permission to be staying there?

Thanks in advance,
Nick