By Andrew MacAskill and Sachin Ravikumar LONDON (Reuters) – London’s police force said the state funeral of Queen Elizabeth will be the biggest security operation it has ever undertaken as prime ministers, presidents and royals come together on Monday to pay their respects to Britain’s longest-reigning monarch. The queen’s funeral is expected to attract hundreds of thousands of people to London’s streets, echoing other important events in Britain’s history, including her coronation in 1953, the funeral of former Prime Minister Winston Churchill in 1965 and the death of Princess Diana in 1997. …