LONDON (Reuters) - British house prices rose at the fastest rate in more than six years at the end of 2020, official figures showed on Wednesday, extending a surge driven by a temporary tax break and demand for more spacious housing since the start of the COVID-19 pandemic. The Office for National Statistics said house prices in December were 8.5% higher than a year earlier, compared with a 7.1% increase in November, the biggest year-on-year rise since October 2014.