Retailers are blaming the wettest April on record for their biggest sales falls for more than a year.
Like-for-like sales dropped by 3.3% in April - the worst performance since March 2011.
The figures released by the British Retail Consortium (BRC) also found April footwear sales were the lowest since 2008.
The trend was made worse because many shoppers had already splashed out on summerwear during the March heatwave.
Online retailers also saw demand slow, while supermarkets felt the pain despite the cold weather boosting sales of winter warmers - hot drinks, porridge, meat for stewing and soup.
However, there was a silver lining as sales of floor coverings and homewares, such as bedding, linen and lighting, received a boost as the depressing weather prompted people to give their homes a facelift.
BRC director general Stephen Robertson said: "The wettest April since records began has put a dampener on retailers' fortunes.
"Consumer interest in summer fashions and outdoor products was washed away by constant downpours."
He said retailers, who have been hurt by the squeeze on consumers' spending power in recent years, are hoping the diamond jubilee, Euro 2012 football championships and Olympics in coming months will boost demand and help the "feel-good factor" return.
The wet weather hit sales of gardening products, such as lawnmowers, plants and tools, but indoor DIY was mixed as people looked to improve their homes but continued to shy away from so-called "big ticket items", such as fitted kitchens and bathrooms.
Online was still the quickest growing part of the retail sector, up by 9%, but its growth slowed from 14% last year.
Mr Robertson added: "You'd think relentless downpours would help online retailing as people shop more at home - and there was some extra interest in gear for cold and wet weather.
"But any gains there were more than offset by consumers switching away from summer goods and by continuing consumer caution."