The Confederation of British Industry's latest distributive trades survey, published yesterday, also signals that the level of employment in the retail sector this month is broadly unchanged from that a year ago.
Subtracting the proportion of retailers experiencing a year-on-year decline in sales volumes in the latest month from that posting a rise, a net 16 per cent reported an increase.
This signalled a much slower pace of increase than the corresponding balance of 30 per cent reporting a year-on-year rise in sales volumes in the April survey. And the year-on-year rise in sales in May was much weaker than had been forecast by retailers. However, a balance of 29 per cent of retailers forecast a year-on-year rise in sales in June.
The CBI survey signals that department stores and specialist food and drink retailers have experienced a sharp year-on-year fall in sales volumes this month.
Grocers have enjoyed a slower but still solid year-on-year rise in sales volumes this month.
Furniture and carpet shops have enjoyed a sharp year-on-year rise in sales in May, but durable goods retailers have experienced a sharp decline in volumes.
Internet sales have shown a solid year-on-year rise, although the pace of increase is the weakest since June 2013.
The CBI highlighted the fact that its survey had now recorded meaningful year-on-year growth in UK retail sales volumes in six consecutive months.
Barry Williams, chair of the CBI distributive trades survey panel, said: "Retailers' predictions of further sales growth bore fruit this month. Although that growth was at a slower rate than expected, the fact we've seen a steady increase for six consecutive months is a sign we're heading towards sustainable growth and strengthening consumer optimism, and it's good to hear shopkeepers telling us they expect even stronger figures next month."
Howard Archer, chief UK economist at consultancy IHS Global Insight, said: "The CBI's survey indicated that retail sales growth slowed in May, although it remained well in positive territory and the underlying trend still looks healthy. Furthermore, consumer confidence is reported to have risen further in May.
"Some slowdown in retail sales growth in May was always likely following recent particularly strong activity, especially in April when sales were boosted by the later Easter this year."