The British Retail Consortium survey for August showed that strong demand for discretionary consumer goods seen earlier in the summer flagged during the month and only food sales lifted.
UK like-for-like sales - which do not include new stores - fell 0.1% compared with the same month last year, said the British Retail Consortium.
Stephen Robertson, director general, British Retail Consortium said: "The strong figures of June and July haven't been sustained. It's clear the deceptively good sales growth of those months was due to summer sun and price cuts."
Non-food, non-store sales, which come from the internet, mail-order and telephone, rose 7.9%, the weakest growth since May.
"This is the second weakest growth we've recorded in the 11 months this measure has been running and [it is] well down on July's figure," said Sharon Hardiman, head of non-store retailing at the BRC.
Separately, data from the Royal Institution of Chartered Surveyors found that rents were falling rather than rising in the three months to July. The study coincides with official data showing rising availability of mortgage finance and modest rises in house prices over recent months, information that could encourage home_owners to sell rather than seek a tenant, RICS said.
"The number of properties coming on to the rental market has slowed as the sales market has begun to stabilise," said Jeremy Leaf, RICS spokesman. "Providing the housing market holds firm, the outlook for the rental market should continue to improve."