Why did Lee Cain’s possible promotion to No 10 chief of staff cause mayhem in Westminster?

John Rentoul on why a report of a new role prompted the resignation of a Dominic Cummings ally

Cain has served as Downing Street’s director of communications since last year (Reuters)

Talk about a bomb in the bubble. The prime minister was “poised” to promote Lee Cain, his director of communications, to chief of staff, it was reported yesterday morning. This detonated a small explosion in the cloistered world of political advisers and journalists in and around Downing Street, and last night Cain announced he was resigning. 

To understand its significance, we need to rehearse the history of the prime minister’s office. The term “chief of staff” was first used in Margaret Thatcher’s time by David Wolfson, the businessman, but it was more of a grand title than an executive office. 

Tony Blair was the first to appoint a chief of staff, Jonathan Powell, as a political appointee to run No 10 in conjunction with the civil service. He served for the full 10 years. David Cameron had a similar administrative linchpin in the form of Ed Llewellyn for all his six years.