LONDON • Britain knows Christmas is coming when John Lewis Partnership launches its television ad. Selling the season as a time for acts of charity rather than any particular product, this year's edition will focus on food poverty and struggling parents. Yet as the coronavirus continues to wreak havoc, it is the department store chain itself that is now a window on the festive period in a country that relies more on consumer spending than any of the big European economies. With a partial lockdown in England closing all non-essential stores until at least Dec 2, rescuing the next six weeks from Covid-19 is critical for Britain's financial well-being and a government beset by accusations that it cannot get a grip on the pandemic. Further disruption to what retailers call the "golden quarter" could be disastrous for an industry that has already been battered. November and December account for one of every £5 of retail spending. The slump during Britain's spring lockdown precipitated the record decline in gross domestic product. It then contributed to most of the recovery in the third quarter reported by the Office for National Statistics on Thursday. The latest lockdown could cost ret...