Brits are spending their cash on clothes and their houses, and less on food
Sales volumes grew in clothing by 41%, and in hardware and DIY by 55%.
But volumes fell markedly for grocers, by 29%.
They also fell in the specialist food and drink sector by 34%, and the footwear and leather sector by 38%.
Overall, the volume of sales decreased. 30% of retailers said that sales volumes were up in September on a year ago, while 38% said they were down, meaning a total balance of -8%.
That was below economists' expectations of +5%. It was also a decline on August's figure of +9%.
It is worth pointing out that the survey is relatively narrow in its scope, as it interviews only 120 firms, of which 63 were retailers. But, as the Financial Times points out, its findings are in line with other data, including John Lewis's weekly sales report and two monthly sales monitors.
Rain Newton-Smith, CBI's chief economist, said: "September is normally an important month for retailers and it's encouraging to see that sales of clothing, DIY goods and hardware are above seasonal norms.
"However, consumer confidence has been dented since earlier in 2016 and higher inflation is likely to squeeze household incomes over the year ahead. With margins remaining tight, retailers are set to continue to operate in a fiercely competitive environment for some time."