To be a 'lawful visitor' to the premises, you must be able to show that you have:
Actual permission – i.e. you were specifically invited to be on the premises. An example would be if you had a pre-arranged business appointment at the premises.
Implied permission – this definition can become a little blurred, but generally comes down to an assumption that a person has permission to be on the premises.
For instance, the purpose of a shopping centre is that it is open to visitors who want to visit shops in the centre, whether to browse or buy from them or visit cafés and restaurants in the centre. Visitors have implied permission to be on the premises for the purposes for which a shopping centre exists.
An exception to this would be if the occupier has specifically barred an individual from visiting the premises due to previous antisocial behaviour whilst on the premises.
Likewise, suppose a visitor to the centre decides not to leave at the designated closing time and hides out of sight until the premises have been locked up for the night. In that case, they immediately become an unauthorised visitor or, in other words, a trespasser.
Lawful right of entry - Examples of visitors with a lawful right to enter the premises include police officers, firefighters, and paramedics attending the premises to perform their duties.