April retail sales suffered their largest monthly drop in values and volumes in a year as cold weather hit the food sector, which recorded its worst sales performance on record.

According to the Office for National Statistics (ONS), April retail sales volumes and values excluding petrol both declined by 1.4% and 1.2% respectively compared with March.

Year-on-year retail sales edged up 0.5% by volume in April while retail sales values jumped 1.3%.

The ONS said the food sector exerted the biggest downwards pressure on both retail sales volumes and values. The major grocers said this was a result of the cold weather which hindered sales of barbecue food and garden furniture.

Year-on-year, the ONS said the quantity of goods purchased across supermarkets declined by 3.8%, the lowest rate since June 2011. The amount spent slipped 0.2%, the largest contraction on record year on year. The level of goods bought has fallen back to its lowest point since December 2003 when the ONS’ index for food was also 93.7.

Against March, food retail volumes slumped 4.1% in April – the lowest level since May 2011. Food sales values also dropped month-on-month by 3.5%.

Online sales sustained a high level, comprising 10% of total retail sales, which the ONS said suggests that consumers were buying online rather than in store due to the unseasonable weather.

British Retail Consortium director general Helen Dickinson said the figures are better than they appear when the distorting effect of an early Easter, which fell in March this year rather than April, is removed.

She added: “The volatile weather conditions in April made this a mixed month for various retail categories. Demand for new-season clothing and footwear lifted with temperatures towards the end of month, a welcome boost after sales suffered during the lingering wintry weather.

“April was a respectable but not spectacular month for sales – retailers will be hoping that more sunshine and the double Bank Holiday boost lifts May’s figures into more positive territory.”