 Middlesex was formerly part of the Kingdom of Essex It was recorded in the Domesday Book as being divided into the six hundreds of Edmonton, Elthorne, Gore, Hounslow (Isleworth in all later records), Ossulstone and Spelthorne.The City of London has been self-governing since the thirteenth century and became a county in its own right, a county corporate.Middlesex also included Westminster, which also had a high degree of autonomy.