LONDON — For a week, Prime Minister Boris Johnson of Britain has denied damaging claims that his staff broke lockdown rules by holding a party last Christmas when such festivities were banned under government-imposed coronavirus restrictions.
Late Tuesday, the government’s story weakened when a video surfaced of senior staff members joking about just such a party four days after they had reportedly gathered to eat snacks, drink wine and play party games in Downing Street.
The revelations have shaken Mr. Johnson’s government, coming just as Britain and the rest of the world enter a second holiday season battered by the emergence of a new variant and faced by anger and frustration from exhausted citizens.
The furor claimed its first casualty on Wednesday when…

