LONDON—British house prices in December were 9.8 percent higher than a year earlier, the sharpest annual increase since the eve of the global financial crisis in July 2007, monthly figures from mortgage lender Halifax showed on Friday. House prices rose by 1.1 percent in December alone, the same increase as in November, and recorded their biggest quarterly rise since November 2006. Britain is not alone among rich economies in seeing a sharp rise in house prices during the COVID-19 pandemic, despite a historic slump in economic output from which it has not yet recovered. Halifax said multiple factors had encouraged people in Britain to buy a new home, including greater demand for space for homeworking, a shortage of other spending opportunities, and a tax break on purchases which expired at the end of September. “A lack of available homes for sale, and historically low mortgage rates, have also helped drive …