Hours after one of Boris Johnson’s longest standing allies quit, with a stinging rebuke of his judgment, the UK prime minister gathered shell-shocked staff in Downing Street to tell them “change is good”.

But while Johnson has tried to put his trademark optimistic spin on yet another week of turmoil, the ebullient persona that carried him to the top is now jarring with the reality of a desperate battle to cling to power.

He started the week with a plan to reinvigorate his premiership, marked by key announcements to flesh out his electoral promise to “level up” forgotten communities, make the most of Brexit and tackle a cost-of-living crisis...