Retail sales fell by 4.4% last month, according to the latest figures from the British Retail Consortium (BRC).
The May figures represent the biggest drop in more than four years, as consumers feel the effects of rising inflation and weak wage growth.
Online sales of non-food items also grew at the slowest rate since records first began in 2012.
Meanwhile, a separate survey conducted by Barclaycard has suggested that consumer confidence reached a new low last month, with 53% of consumers reporting that they feel confident about their finances, compared with 70% in March.
According to the survey, growth in consumer spending fell to 2.8% in May, with spending on households goods and clothing falling by 2.9% when compared to the previous year, although spending on cinemas and eating out rose by 11.5% and 11.7% respectively.