The Protection from Eviction Act 1977 makes it a criminal offence for any person to unlawfully deprive a 'residential occupier' of their occupation of the premises. Unless the tenant agrees to vacate, the only legal way a landlord can evict a tenant is by obtaining a court order. Any term in the tenancy agreement that says otherwise will be void.
Landlord Rehan Sheikh was sentenced to four months in jail after giving six tenants a two-hour warning that he was going to evict them after they complained about the condition of their shared home.
If a person returns to find a trespasser in their home, it is an offence for the trespasser to refuse to leave if required by a "displaced residential occupier" (s7 Criminal Law Act 1977); therefore, they should call the police.