LONDON: Britain’s retail sales sank in December by the biggest amount in more than a year as unseasonally mild weather conditions hit clothing demand over Christmas, official data showed on Friday. Sales by volume dropped one per cent last month compared with November, the Office for National Statistics said in a statement. That was the largest drop since September 2014 and was worse than market expectations for a 0.3 per cent decline. Retail sales had jumped by 1.3 per cent in November, helped by buying on ‘Black Friday’ when items are heavily discounted in the run-up to Christmas.