rent arrears?

i currently owe my landlord £600 in rent arrears im paying him back an extra £25 ontop of my rent monthly hes now threatenin me on the phone sayin he wants £50 per month extra not£25 if not i can get out ,my tenancy agreement ran out beginin of sept just wonderin wha my rights are oh an by the way my landlord is my father ive been here 5 yrs