Experian said its monthly footfall index showed shopper numbers fell 2.6% in June from the same month last year, and were down 5.8% to out-of-town destinations.
UK internet traffic to retail websites, in contrast, was up 6.5% on the year, with price-conscious shoppers searching for 'sales' at the highest rate since Christmas.
"The reduction in visits to out-of-town centres is having a significant impact on retail sales," said Experian director of retail consultancy Jonathan de Mello. "People generally drive to out-of-town destinations with a specific large purchase in mind and there is far less browsing than is the case in town centres."
The figures come just days after Sir Stuart Rose, chief executive of Marks & Spencer, claimed that Britain's high streets were benefiting from petrol hikes as customers chose to walk to local shops. He said: "If a tank of petrol costs £40 more than it did, are you going to drive to Bluewater or walk down the high street?"