The prime minister’s office has clashed with the UK’s Health Security Agency chief over her recommendations for people to socialise less before Christmas — going beyond the official guidance — with a Number 10 spokesman stating “she is not a government minister”. On Saturday, Prime Minister Johnson announced the reintroduction of the mask mandate in shops and public transport with other traveller restrictions over concerns of the new Omicron variant of the Chinese coronavirus, saying that the measures would be reviewed in three weeks’ time, not long before Christmas.