FILE - In this file photo dated Tuesday April 28, 2020, Britain's Prime Minister Boris Johnson, centre, Chancellor of the Exchequer Rishi Sunak, right, and Cabinet Secretary Mark Sedwill stand inside 10 Downing Street, London, during a minute's silence to pay tribute to the NHS staff and key workers who have died during the coronavirus outbreak. Britain’s top civil servant Mark Sedwill announced Sunday June 28, 2020, he will resign from his role as Cabinet Secretary, national security adviser and head of the Civil Service in September 2020. (Stefan Rousseau/Pool via AP)

FILE - In this file photo dated Wednesday, May 8, 2019, Britain's National Security Adviser Mark Sedwill shakes hands with Chinese Foreign Minister Wang Yi, right, in Beijing. Britain’s top civil servant Mark Sedwill announced Sunday June 28, 2020, he will resign from his role as Cabinet Secretary, national security adviser and head of the Civil Service in September 2020. (Florence Lo/Pool FILE via AP)