Sales for non-food stores rose 3.9%, the largest increase for 17 years. This was mainly driven by textile, clothing and footwear stores, which recorded a rise of 9.2% driven by the warm weather during the month.
The average weekly value of sales in May was £5.3 billion, 7% per cent higher than in May the previous year.
Sales volumes in the three months to May rose by 1.8%, compared to a 1.5% rise in the three months to April.
Richard Lowe, corporate Director of the retail and wholesale sectors, Barclays Commercial Bank commented: "After a gloomy Easter, the sun has shone for retailers this May...These surprisingly strong results come as a result of pent-up consumer demand following the post-Christmas hangover and cautious spending earlier this year. With the bout of good weather, retailers saw summer spending habits arrive early, boosting sales without the need to squeeze their margins by setting restrictive discounts. It is likely that the increase in footfall has encouraged retailers to push back the launch of their summer Sales."
Lowe added: "Today's statistics are a welcome moment of relief in an otherwise challenging time for UK retailers. However, prospects remain highly uncertain as real household incomes come under pressure with rising rates of inflation."