A Page of the Backstairs is today a senior servant of the British Royal Household who personally attends to the Sovereign and/or spouse (presently Queen Elizabeth II of the United Kingdom and Prince Philip, Duke of Edinburgh). In the past they were far more junior page boys, often of modern school age.
As of 2009, there are three Pages of the Backstairs, including:
Their duties include serving meals and tidying personal apartments. They also grant access to other members of the Household into The Queen and Prince Philip's private rooms and their office is situated near to the backstairs of Buckingham Palace and The Queen's lift.
References
Page of the Backstairs Wikipedia(Text) CC BY-SA