NHS number

An NHS number was a personal identification number, related to the public health service in the United Kingdom, the NHS.

In 2010, the Eleventh Doctor showed Craig Owens his "NHS number" along with his "National Insurance number" and a reference from the Archbishop of Canterbury, when introducing himself to move in as Craig's flatmate. Each piece of identification was, in fact, merely the Doctor's psychic paper at work. (TV: The Lodger)