LONDON — A horse-drawn gun carriage bore the coffin of Margaret Thatcher to St. Paul’s Cathedral on Wednesday for a ceremonial funeral that divided British opinion, much as the former prime minister known as the Iron Lady stirred deep and conflicting emotions during her lifetime and, in death, triggered an equally passionate debate over her legacy.

With hymns and prayers and biblical readings, dignitaries from around the world and from Britain’s political elite gathered in the cathedral for a service regarded as austere and devout reflecting her Methodist upbringing as bells pealed over the city and a gun salute boomed from the Tower of London.

Some 700 military personnel from three services — the Army, Royal Navy and Royal Air Force — lined the streets, including guards in scarlet tunics and distinctive black bearskin hats on the 24 cathedral steps as the gun carriage processed along Fleet Street and Ludgate Hill from the church of St. Clement Danes in a closely scripted display of ceremonial precision honed over centuries....