The UK's High Street shops had a disappointing time last month, according to the latest set of official figures.
Shoppers are more reluctant to spend
Retail sales fell by 0.1% from April, the Office for National Statistics (ONS) said, the weakest performance since January's 1% drop.
The fall caught analysts by surprise, as most had been expecting sales to rise during May, and led to further speculation about a possible cut in interest rates.
There was more bad news for the UK economy from employers group CBI after it found little sign of any pick-up in the manufacturing sector.
Retail sales have been expected to slow since April when increases in national insurance contributions and council tax took effect.
In the three months to May, retail sales grew by 0.5% compared with the previous three months and by 3.4% compared with the same period last year.
The 3.4% annual increase was the weakest growth rate since July 1999, adding to the growing evidence that the UK consumer boom is over.
"Retail sales have shown a drop on the month helping to confirm the general story that consumer spending growth is slowing down," said Philip Shaw at Investec.
"With sterling firm and inflation falling, this may
well lead to the Bank of England bringing rates down at July's meeting."
The Bank last cut rates at its February meeting when they fell to a 48-year low of 3.75%.
The CBI issued another plea for lower interest rates after their latest snapshot of the beleaguered manufacturing sector found little sign of improvement.
Of those firms surveyed, 39% of firms said orders were below normal, against 12% reporting an improvement.
The balance of minus 27% is only slightly better than the previous month's figure and the CBI said exporters had yet to see any benefit from the weaker pound.
"Demand at home and abroad remains persistently weak and output continues to stagnate," said Doug Godden, head of the CBI's economic analysis.
"Companies are cautious about the future and with no danger from inflation, an interest rate cut remains appropriate."
While the ONS data indicated conditions were getting tougher for retailers, separate figures from the British Bankers' Association (BBA) suggested people were still spending more on their credit cards.
The BBA figures showed credit card lending increased by about £500m last month.
Figures from the BBA also showed that mortgage lending grew at a slower pace in May.
Underlying mortgage lending increased by £4.6bn last month, compared with £5.2bn in April.