Beverage prices across the big four supermarkets fell in June, marking the first month-on-month price drop this year.

In the four weeks to 26 June, average prices dropped by 0.2%, according to The Grocer Price Index compiled by The last time prices fell was back in December when the supermarkets slashed alcohol prices by 5% in the run up to Christmas and New Year.

Alcohol was instrumental again this time. The supermarkets encouraged customers to stock up on booze for the jubilee weekend and Euro 2012 by cutting alochol prices by 2.4% on average. Asda led the way, slashing the price of booze by over 5%.

In the same month Asda was crowned lowest priced supermarket for the 15th consecutive year, at The Grocer Gold Awards 2012, the booze promotions helped to bring down Asda’s category-wide prices by 1.6% month-on-month and limited overall annual inflation to 3%. Once the impact of promotions was removed from the comparison, Asda’s prices were just 0.7% higher than a year ago.

It was the other way around at its arch rival Tesco. At 2.7%, inflation at the tills, once promotions were factored in, was slightly lower than at Asda. However, comparing prices before promotions were added in and Tesco’s inflation was substantially higher at 3.4%.

It is a case of contrasting fates in global prawns. While coldwater species have continued to rise in price, up 17.1% month-on-month to £4,380/t - 53.4% higher than this time last year - warmwater prices have fallen nearly 17% to £2,634/t. The latest month-on-month drop means they are 30.5% cheaper than in June last year.

Warmwater prawn prices have been falling despite fears earlier this year that possible changes to Thailand’s EU import tariffs by the World Bank could soon spell higher prices for EU buyers. Prices had also risen slightly over concerns that Vietnam could struggle to recover from a disease outbreak that wiped out 5% of its total black tiger shrimp production.

On the coldwater side, declining stocks - driven down in part by invasive, prawn-eating cod species around Greenland - are set to keep supplies tight - with high prices to match.

But when it comes to keeping a lid on inflation, it was Waitrose that has kept prices down the most, albeit from a higher base. After extending its Brand Price Match scheme to all branded groceries in May, Waitrose’s prices fell 4.2%, and despite a small month-on-month increase in June, annual inflation at Waitrose is still running at just 1.6%, which is substantially lower than at any of its bigger rivals. Average prices factoring in promos across the big four were 3.7% higher than last year, with Morrisons and Sainsbury’s hiking prices by 4.3% and 4.5% respectively.

Sainsbury’s was the only big four supermarket to increase its prices month-on-month - by 1.35%. One reason for this was the fact that, unlike its rivals - including Waitrose - Sainsbury’s did not offer its customers big discounts on booze.

It also hiked the price of baby and household products by 4.2% and 7.4% respectively. These were also the categories to increase in price the most across the supermarkets. Baby product prices increased the most, rising by an average of 4.3% month-on-month.

Year-on-year, the category to increase in price the most was soft drinks - shooting up 10.4% on the back of higher cost of goods, notably sugar and PET. Only tobacco and frozen food came close to that level.