The drop was due to a fall in sales volumes in non-food stores, with lighting and furniture businesses the hardest hit, according to the UK-wide numbers from the Office for National Statistics (ONS).
Sales volumes in September were down 0.2 per cent, following a 0.6 per cent fall in August, although they remain 4.2 per cent above pre-pandemic levels in February 2020.
Fuel sales rose in the final weeks of September as panic buying led to many forecourts running dry after suppliers said the HGV driver shortage was affecting deliveries. Fuel sales rose 2.9 per cent.
Food sales volumes were up by 0.6 per cent, the ONS added, and remain 3.9 per cent above pre-Covid levels.
But while shoppers opted to avoid high streets, sales online continued to rise and now account for 28.1 per cent of all spending - up from 27.9 per cent in August. There was a particular surge in department store sales online, up by 3.8 per cent.
Darren Morgan, ONS director of economic statistics, said: "Household goods were the main driver of this month's decline, with a fall of nearly 10 per cent, while food sales ticked back up after falling last month.
"Petrol sales exceeded their pre-pandemic level for the first time, with filling stations reporting very strong sales during the last week of September.
"Despite the lifting of restrictions, in-store retail sales remain subdued, with many consumers still opting to shop online."
Lisa Hooker, consumer markets leader at PwC, said the headline sales numbers “hide a multitude of sins”.
She added: “Not least with September’s spending patterns dominated by the petrol crisis, and the subsequent increase in fuel sales, which diverted attention away from the high street.
“Grocery and clothing sales saw some pick-up as families stocked up ahead of both back-to-school and back-to-the-office. However, most other categories declined slightly.
“Despite September’s slowdown, we are still confident about retail’s prospects ahead of the all-important Golden Quarter in the run-up to Christmas. Consumers still tell us that they have money in their pockets.”
Susannah Streeter, senior investment and markets analyst at financial services group Hargreaves Lansdown, noted: “The snap back in sales in bricks and mortar stores has also faded, with the novelty of a trip to the high street wearing off.
“More of us have gone back to our pandemic habits of ordering with an on screen click rather than a trip to the shops.”
Helen Dickinson, chief executive of the British Retail Consortium, said: "Retailers will be concerned by the slump in sales, just as they begin their preparations for the all-important Christmas period.
"Fuel shortages, wet weather and low consumer confidence all contributed to lower consumer demand this month, with household goods, furniture and books all hit particularly hard.
“For the sake of the UK's economic recovery, it is vital that retail sales bounce back as we near the festive season.”