LONDON—Spending by British consumers plunged in January at the fastest rate in seven months as the country went back into a tight COVID-19 lockdown, payment card firm Barclaycard said on Tuesday. A 73 percent annual increase in online retail spending and record demand for takeaway food—which jumped by a third from a year ago—failed to compensate for the closure of many businesses. Overall consumer spending shrank by 16.3 percent in year-on-year terms last month, Barclaycard said, the biggest drop since May when the country was starting to emerge from its first lockdown. Spending in pubs and bars dropped nearly 94 percent and was down by more than 84 percent in restaurants, the survey showed. Travel agents also reported an 87 percent drop in spending during a month when many Britons would normally book summer holidays abroad. By contrast spending at supermarkets soared by 17 percent as people prepared more food …