Retail food and drink prices at the big four fell month-on-month for the first time in 2008 - but wholesalers claim suppliers are being forced to pick up the shortfall with price hikes.

The Grocer Price Index shows that prices at the multiples in October fell slightly, down 0.1% month-on-month - the first actual fall this year - compared with an uplift of 1.1% in September.

Much of the reason for the supermarkets' fall in prices has been due to cheaper alcohol prices.

However wholesalers claimed drink suppliers were not offering the same discounts so they have been unable to compete and claimed this was further evidence of the waterbed theory. "While these prices are clearly dropping in supermarkets, ours are not," said one leading wholesaler. "It seems unlikely that the multiples are absorbing the price increases," said another wholesaler. "More likely they are putting massive pressure on suppliers to drop prices despite rising costs. Wholesalers don't have the power to do the same, so we are absorbing the extra cost."

According to the latest The Grocer 33 figures, Budweiser, Stella, John Smith's Extra Smooth, Smirnoff and Jacob's Creek shiraz rosé have all fallen in price at the supermarkets in the last month. But wholesalers claimed these prices had not fallen in their sector.

A Diageo spokesman said it did not set or agree retail prices for its brands.

Of the multiples, Asda showed the largest fall in its prices, down 1.5% on September. Prices started falling at Asda earlier than its rivals, down 0.1% in September.