The original Scotland Yard was an area near Westminster Palace occupied by the Scottish Ambassador to the English court. Later an office block was built on the same spot and took the name Scotland Yard.

When it was demolished and a new office block was erected on the same spot it was called New Scotland Yard.

So the old Scotland Yard is beneath the foundations of New Scotland Yard!

Not sure what you mean. Scotland Yard is the name of a street in London. The Headquarters of the Metropolitan Police are known as New Scotland Yard (although they're not located there) but the majority of people just call it Scotland Yard.

Scotland Yard (actually, New Scotland Yard) is the headquarters of the London Metropolitan Police Service. Their mailing address is:

Metropolitan Police Service

New Scotland Yard

Broadway

London, United Kingdom

SW1H 0BG

an inspector from Scotland Yard

Scotland Yard was created in 1829.