The survey of 117 firms showed that orders placed on suppliers also fell over the year, while sales for the time of year were considered to be average. Sales are expected to rebound next month, while orders are set to fall at a broadly similar pace.
Within retail, department stores and the clothing sector were the main drivers behind the fall in sales. Performance also deteriorated in the durable household goods sector and in footwear and leather goods.
Meanwhile, growth in the volume of internet sales slowed in the year to April, with the survey balance falling further below the long run average. Internet sales growth is set to pick up slightly in May.
CBI director of economics Rain Newton-Smith said: "Cold weather put a chill in sales of spring and summer ranges with a reported dip in retail sales in the year to April, but with the near-term outlook for household spending holding up the sector expects a modest rise in sales next month.
"However with margins remaining tight within the sector, retailers will continue to operate in a fiercely competitive environment for some time."
Some 22 per cent of retailers said that sales volumes were up in April on a year ago, whilst 36 per cent said they were down, giving a rounded balance of -13 per cent. This indicated a fall in sales from the previous month (+7 per cent). Sales growth is set to rebound in the year to May (+9 per cent), although it remains below the long-run average of +24 per cent.
Some 21 per cent of retailers reported sales volumes to be good for the time of year, with 21 per cent reporting them to be poor, giving a balance of 0 per cent - broadly in line with the long-run average of -1 per cent.
Meanwhile, 52 per cent of wholesalers reported sales volumes to be up on last year and 19 per cent said they were down, giving a balance of +33 per cent. Wholesalers expect sales to rise further in May 2016 (+41 per cent).
Meanwhile, the British Retail Consortium reports that the equivalent number of full-time jobs fell by 0.9 per cent in the first quarter of 2016 compared with the same period last year.