The Office for National Statistics (ONS) said retail sales volumes dropped by 2.5% between June and July 2021 but remain 5.8% ahead of pre-pandemic levels.
It said this was partly driven by a decline in food store sales which were impacted by customers returning to hospitality venues and the end of the Euro 2020 football tournament.
The figures come significantly below the expectations of analysts, who had forecast an increase of 0.2% for the month.
Food store sales slipped by 1.5% for the month, while non-food stores, such as fashion chains, reported a 4.4% decline in volumes.
Jonathan Athow, deputy national statistician for economic statistics at the ONS, said: “Following the Euro 2020-related boost in June, retail sales fell in July to their lowest level since shops reopened in April, but still remain well above pre-pandemic levels.
“Food sales fell back as further lifting of hospitality restrictions meant consumers had more opportunities to spend outside retail.
“Heavy rainfall at the start of July hit fuel sales, which dipped for the first time since February.”