LONDON, May 21 (Reuters) - British retail sales climbed by 9.2% in April, when non-essential shops reopened after months of closure due to COVID restrictions, a bigger increase than economists had expected, official data showed on Friday. Sales volumes were 42.4% higher than a year earlier, when sales volumes collapsed during Britain’s first coronavirus lockdown, the Office for National Statistics said. Economists polled by Reuters had on average forecast that retail sales volumes would rise by 4.5% on the month in April and surge 36.8% on the year. (Reporting by David Milliken and Andy Bruce) Our Standards: The Thomson Reuters Trust Principles.