It isn't the "Police Department", as neither England nor Britain have police departments. There are regional constabularies, for example, where I live it is Cambridgeshire Constabulary http://www.cambs.police.uk/ Scotland Yard is simply the address of the headquarters of the Metropolitan Police http://content.met.police.uk/Home , which covers most of Greater London. The original building was built on a street called Scotland Yard, then, when it was replaced with a new building it was called "New Scotland Yard".