Rishi Sunak faces fresh pressure to crackdown on supermarkets as families battle sky-high food prices.
Store bosses and farming chiefs are being hauled into No10 on Tuesday for crisis talks amid mounting anger as households are hit by rocketing inflation.
A Lib Dem analysis of official figures, seen by the Mirror, revealed how customers face higher prices in stores even if costs have fallen.
The party said a loaf of wholemeal bread has gone up 26%, despite the cost of breadmaking wheat having dropped by 14%.
Shelf prices of apples are yet to fall despite wholesale costs falling 45%.
The supermarket price of tomatoes has soared up by 13% when farmers have dropped prices by 7%.
Store prices of potatoes have climbed 13% even though farmers have not hiked prices, while the cost of eggs in shops has risen 23% while wholesale prices only increased by 11%.
Lib Dem leader Sir Ed Davey said: “The cost of the weekly shop is soaring while supermarkets rake in eye-watering profits.
“But Rishi Sunak is so out of touch he hasn’t lifted a finger to help families on the brink.
“We need tough measures now to get food costs under control and put pressure on supermarkets and food multinationals to bring their prices down more quickly.
“Anything less would make this Downing Street summit nothing but a pointless talking shop.”
The Scottish National Party accused the Tory premier of presiding over supermarket “greedflation”.
Its social justice spokesman David Linden said: "The Tory Government is deliberately sitting on its hands while families suffer from soaring food prices, greedflation and a cost-of-living crisis that has spiralled out of control.
“The Prime Minister must finally take tough action to lower prices in shops, launch an investigation into price gouging and ensure inflation is not used as an excuse for profiteering.”
Official figures show food and drink inflation reached 19.1% in March, almost double the 10.1% overall rate.
Retailers have warned of a three to nine-month delay between production costs falling and shelf prices being cut.
The British Retail Consortium said last month: "As food production costs peaked in October 2022, we expect consumer food prices to start coming down over the next few months.”
The situation got so bad that Mr Sunak decided to call Tuesday's Downing Street summit.
The National Farmers’ Union warned the meeting needs to deliver "actions, not just words".
President Minette Batters said: “We are calling on government to make this an annual summit which would mark a turning point in how previous governments have prioritised the safe and affordable supply of sustainably produced home-grown food.
“The past 18 months have been a stark reminder of how vulnerable the nation’s food security is.
“It has been a wake-up call for the importance of a secure domestic supply of food, and it is vital that the summit delivers actions, not just words.”
Some campaigners have hit out at the meeting going ahead without a planned horticultural strategy - axed by the Government.
Food Foundation executive director Anna Taylor said ensuring resilient future supplies of fruit and vegetables should be a key part of the summit.
"It was extremely disappointing to see the recent U-turn on producing a horticulture strategy,” she said.
"The strategy presented a chance to create long-term, joined up policies to support the threatened UK horticulture sector to reach its enormous potential, as well as an opportunity to secure better health outcomes for citizens by ensuring we have enough affordable fruit and veg."
The Soil Association said scrapping plans for a horticulture strategy was “a major disappointment, coming at a time when citizens are facing empty shelves”.
A spokesman added: “Our farmers are struggling with fuel and electricity costs, labour shortages and dangerously low profits – with many considering throwing in the towel.
“With a delayed growing season in the UK and the threat of droughts abroad it’s likely we’ll face the same issues again.”
Andrew Opie, director of food and sustainability at the British Retail Consortium, said: “With food production costs rising significantly over the last year owing to high energy costs, global food prices, and labour shortages, we have seen a knock-on impact to prices on the shelves.
“As these costs begin to fall, we expect to see food price inflation falling away in the coming months.
“Government can also play a role by minimising the financial impact of some incoming regulations, such as its deposit return scheme and reforms to extended producer responsibility, that might otherwise increase costs for consumers.”
A Government spokesman said: “Our UK Farm to Fork summit will bring together government and representatives from across the food supply chain to step up cooperation and promote all elements of our world renowned farming and food industries.
“The event will look at how we can champion UK food and drink both at home and abroad by boosting confidence, helping more businesses to invest in domestic production and supporting the long-term resilience and sustainability of the UK food sector.”
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