The Lord Mayor’s Show is an annual London event on the 2nd Saturday in November.

“It all begins with the ancient and justified caution of King John. He tried to win London’s support by allowing it to choose its own Mayor, but he insisted that immediately after election the Mayor must leave the safety of the City of London, travel upriver to distant Westminster and swear loyalty to the Crown.
Over the centuries this inconvenient journey became one of London’s favourite rituals. It moved from river barges to horseback and then into the magnificent State Coach, and around it grew a rowdy and joyful mediæval festival that became known as the Lord Mayor’s Show.”
http://lordmayorsshow.london

Get more information about it on the City of London website.

Learn about the The Lord Mayor of London’s State Coach on the Museum of London blog and website.

Two London parades compared on the British Council website
That lesson compares two of London’s biggest parades : the Lord Mayor’s Show, which originates from the same time as the Magna Carta, in 1215, and the Notting Hill Carnival, which has been held every year since 1966 and is one of the largest street festivals in the world.