Footfall dropped by 1.1% in August compared to 2013, despite sales for the month rising.
The high street was the worst affected area, down 2.8% year on year, which was the sharpest decline since February 2014.
According to data from Springboard, shopping centres were also hit with footfall down 1.1% on August last year. Retail parks saw the only rise of the month, up 2.9% on 2013.
British Retail Consortium director general Helen Dickinson said the disparity between footfall and sales levels showed customers are spending more during each trip when they go shopping.
“It seems that customers are hitting the high streets with purpose – knowing what they want to buy ahead of time, supported by online research – and doing more shopping in a single trip,” she said.
Diane Wehrle, retail insights director at Springboard, said the drop in footfall in August across high streets and shopping centres showed the “vulnerability” of these areas as a result of online shopping.
She added: “The good news is that while footfall dropped, sales rose in August, primarily driven by clothing and footwear - traditionally town centre focused purchases - indicating that at least in part the drop in footfall will have been offset by increased dwell time and transaction values.”