UK retail sales values fell 1.5% compared with April 2007.
"The year-on-year declines in March and April were the worst since Spring 2005," said the BRC's report.
Stephen Robertson, its director general, said: "This is the first time in three years we’ve had two months in a row of year-on-year falls in like-for-like sales, further evidence that hard-pressed customers are really watching the pounds.
"With higher fuel and utility bills eating away at people’s spare cash, they are concentrating on essentials like food.
"Despite heavy discounting, clothing and footwear were at their weakest for at least eight years and more expensive housing-related goods continue to struggle."