Britain's biggest security operation

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An extraordinary group of world leaders will gather on Monday for the funeral of Queen Elizabeth II. It will bring together an Emperor; several Kings and Queens; numerous Presidents and Prime Ministers; Princes, Dukes and Duchesses; Archbishops; Generals, Admirals and Air Marshals. Tens if not hundreds of thousands of people are expected in Central London, wanting to be part of the occasion. So how do you protect everyone and what is being done to get ready for what might be Britain's biggest security operation? BBC Home Affairs Correspondent Daniel Sandford answers 5 key questions. Image credit: Reuters