Overall sales fell by 0.8% over last year, a contrast to April when sales were buoyed by sunny weather, the BRC says.
It reports that food sales slowed after an April boosted by Easter, although they were up 5.4% for the three months March-May compared to last year.
Non-food sales were down 2.4% over the three months, reflecting an “extremely difficult spring” for most non-food retailers, according to the BRC.
It adds customers are still avoiding “big ticket” items such as furniture and electricals, which is a sign confidence in the economy is still very low.
Meanwhile non-store sales, which include online, were the weakest they have been since the BRC started monitoring the category.
This shows such retailers “are not immune from the impact of the recession”, although they are continuing to outperform traditional retailers in growth terms with a 7.6% rise in sales over the three months, it says.
“Sun and bank holidays don’t a recovery make,” says BRC director general Stephen Robertson.
“However this May was always going to be difficult because the comparison with strong is with strong May sales last year which delivered some of 2008’s best growth figures,” he added.