The UK's High Street shops had a disappointing time last month, according to the latest set of official figures.
Retail sales fell by 0.1% from April, the Office for National Statistics (ONS) said, the weakest month since January.
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.
However, retail sales have been expected to slow since April when increases in national insurance contributions and council tax took effect.
More: The BBC