The figure from Worldpanel by Numerator (formerly Kantar), which provides an early indication of pricing pressures ahead of official UK inflation data on October 22, compared with 4.9% in last month's report, Reuters reported.
Worldpanel said prices were rising fastest in markets such as chocolate confectionery, fresh meat and coffee and falling fastest in household paper, sugar confectionery and sparkling wine.
Britain's food retailers have said that higher employer taxes and regulatory costs as well as increased staff wages are adding to inflationary pressure from higher prices for commodities.
The British Retail Consortium, which represents Britain's biggest retailers, predicts that food inflation will be up to 6% by the end of the year, putting more pressure on household budgets in the run up to Christmas.
The Bank of England has forecast it will hit 5.5% before Christmas and then fall back as global wholesale factors fade.
Overall UK inflation held at 3.8% in August, according to official data published last month, the highest among major advanced economies.
Worldpanel said grocery sales rose 4.1% over the four week period year-on-year.
Separate industry data published on Tuesday showed British consumer spending grew by the least in four months in September as uncertainty ahead of finance minister Rachel Reeves' budget next month and rising energy bills deterred shoppers.