The Mitre Tavern, between Hatton Garden and Ely Place. It bears a stone mitre carved on the front with the date 1546. Ely Place still has its own Watchman who closes the gates a ten o’clock and cries the hours through the night.
It comes as no surprise that the three headed hound belongs to Rubeus Hagrid who is renowned as having a penchant for collecting dangerous beasties. When being verbally grilled by the three young wizards, Hagrid boasts about how he acquired the guard-dog from a “Greek chappie” he met in the pub. It then becomes clear that Fluffy is intended to be Cerberus of Greek Mythology – the three headed dog which guards the gates of the Underworld. (Harry Potter and the Sorcerer's Stone)