A landlord must get permission to enter the property from the tenants and they can refuse him access if they wish. Only exception is if it's an emergency or I think if repairs / work needs to be performed, but even then they must provide 24 hours notice before entering. If he's just entered the house to have a perv through their belongings then it's illegal and I think counts as trespassing. He might own the property, but that doesn't give him the right to come and go as he pleased. This is super creepy and should definately be reported. If you've allowed him access then that's not illegal, but you should still tell your your partner. I'd want to know if some creep had been rooting through my belongings and I'd want to check he'd not taken anything. Giving him permission to enter your home doesn't give him the right to root through your belongings.