Historians working on the restoration of the House of Commons discovered the 360 year-old forgotten passageway hidden in a secret chamber.
They decided to investigate after they found plans for a staircase to a doorway behind the cloister of the Westminster Hall. A tiny brass key-hole in the panelling of the cloister revealed the secret passage.
It was created as the entrance to the celebratory banquet for the coronation of Charles II (1660) in the Westminster Hall located near the modern day House of Commons. It was later used as the main entrance to the House of Commons by generations of MPs before being blocked.
The uncovered passage revealed a wooden panelled Tudor cloister with electrical lighting which was probably installed in 1950, the last major restoration of the Westminster Palace after World War 2.
To find out more about the secret passage, log on to BBC.