The new head of the Metropolitan Police starts work on Monday during what is arguably one of the most turbulent times to face Britain’s biggest police force.Sir Mark Rowley takes over as Commissioner at Scotland Yard after former boss Dame Cressida Dick resigned in controversial circumstances earlier in the year.The force has been plagued by a series of scandals and missteps in recent years, leaving Sir Mark with the task of rebuilding public confidence.It was placed in a form of special measures by a watchdog earlier this year.