 The mayor of London has a range of responsibilities covering policing, transport, housing, planning, economic development, arts, culture and the environment, controlling a budget of around £17 billion per year.Mayors are elected for a period of four years, with no limit to the number of terms served.Under the Greater London Authority Act 1999, mayoral elections are held on the first Thursday in May in the fourth calendar year following the previous election, unless varied by an order by the Secretary of State.