British retail sales volumes fell by a sharper than expected 0.9% in September compared with the month before, latest figures from the Office for National Statistics showed.
Economists polled by Reuters had forecast that sales volumes would fall by 0.2% on the month.
Compared with a year ago, sales volumes were down 1.0%, while sales in the third quarter overall - which had a weak start due to unusually wet weather in July - were 0.8% lower than in the quarter before.
British households have faced a cost-of-living squeeze over the past two years due to supply-chain difficulties and labour shortages after the COVID-19 pandemic, amplified by a surge in energy costs after Russia invaded Ukraine in October 2022.
While retail sales volumes surged in mid 2021 when shops fully reopened in Britain after COVID-19 restrictions, purchases have steadily fallen since and for the past year sales volumes have been below pre-pandemic levels.
Earlier this week, CPI data showed that food inflation in the UK fell to 12.1%, with prices dropping 0.2% between August and September.
The British Retail Consortium said the decline will be "particularly welcome" for shoppers as they head into the winter months.
Helen Dickinson, CEO of the British Retail Consortium (BRC) said that the drop in food prices reflected the "fierce competition between retailers, their investment in cutting costs, and the fall in the price of some global commodities".