LONDON — British Prime Minister Boris Johnson has appointed a former Treasury official and management consultant as his chief of staff, as he tries to restore calm after a tumultuous period for Downing Street.

Johnson's office said Thursday that Dan Rosenfield will take up the post Dec. 7. Rosenfield most recently worked at business consultancy Hakluyt, and formerly at Bank of America and as an aide to past U.K. Treasury chiefs Alastair Darling and George Osborne.

The appointment comes after the departure this month of Johnson's powerful chief aide, Dominic Cummings, and communications director Lee Cain, who quit amid reports of power struggles inside the prime minister's 10 Downing St. office.

Cummings and Cain were key players in the 2016 campaign to take Britain out of the European Union and helped Johnson win a decisive election victory in December 2019. But their combative style toward civil servants, lawmakers and the media made many enemies. Their departure has triggered a series of personnel changes at No. 10.

These include a new press secretary, former journalist Allegra Stratton, to hold televised daily Downing Street news conferences.