@D.B.Moody has it! My aunt works in the House of Commons, so I took this when I stopped by to see her in 2018. For those who don't know the history of the building, the UK government says:
Westminster Hall is the oldest building on the Parliamentary estate. What makes it such an astonishing building is not simply its great size and the magnificence of its roof, but its central role in British history. In and around the Hall, grew up the major institutions of the British state: Parliament, the law courts and various government offices. Closely involved in the life of the nation since the 11th century, a journey through the Hall's past is a journey through 900 fascinating years of our history.