The original Temple Bar marked the boundary between the old City of London and the royal area of Westminster. A gate was built there, but this was removed in the 19th century for road widening. The spot is now marked by a Victorian memorial in the middle of the Strand/Fleet Street, close to the Royal Courts of Justice. Temple Bar Gate, after a period of decorating a country house in Hertfordshire, is now in the south-east corner of Paternoster Square, next to St Paul's Cathedral (EC4). The featured article will give you the full story, more or less.
Post code is approximate for the memorial at Temple Bar.