The UK food industry has begged the government to avoid a no-deal Brexit, warning it could lead to food shortages and price rises. Nearly a third of the food Britons eat comes from the EU.

In March, when the UK is set to exit the trading bloc, the proportion is far higher because most British crops are not yet ready to harvest. According to the British Retail Consortium, during the month of March 90% of the lettuces eaten in the UK, 80% of the tomatoes and 70% of soft fruit is sourced from the EU.

The fear is that long delays at ports, the introduction of high import and export tariffs and a lack of migrant workers to pick and process food could not just be highly disruptive, but sound the death knell for some British farmers, producers and retailers.

Even the pro-Brexit environment secretary, Michael Gove, has admitted delays were likely in Calais – the port that handles most food heading from the EU to the UK – due to mandatory EU checks on food exports from the UK on the French side of the channel. That, he said, would have a knock-on effect on trucks and the turnaround of ferries heading back to the UK.

On Tuesday he told the National Farmers’ Union annual conference in Birmingham that reports suggesting Britain would operate a zero-tariff regime in order to secure frictionless trade in a no-deal scenario were “not accurate”. He said the tariff regime Britain would like to apply in the event of no deal – most probably on meat, and especially lamb – would be revealed in the “next few days”.

Gove promised British food standards would not be lowered “in pursuit of trade deals”, but UK producers fear a wave of lower standard imports – particularly from the US – could undercut them and reduce quality for shoppers.

Retailers usually have only a few days’ food supplies in their distribution centres if they are not kept topped up. They have been stockpiling packet, tinned and frozen foods and are examining ways to increase the shelf life of the most perishable goods, taking on more chilled storage capacity and using varieties of perishables that last longer.

Three-quarters of warehouse owners say their space is now full to capacity, according to a January survey by the UK Warehousing Association, whose 750 member operate 9.3m sq metres (100m sq ft) of space across the country. It is understood that frozen and chilled food warehouses, storing everything from garden peas to half-cooked supermarket bread and cold-store potatoes, are now fully booked until beyond April.

But many company chiefs privately admit their main policy is to cross their fingers and hope that the UK signs a deal with the EU as soon as possible.

Retailers

Marks & Spencer. Photograph: Dan Kitwood/Getty Images

Tesco and Marks & Spencer

Both major retailers have said they are working with suppliers to stockpile packet and tinned foods. Tesco boss, Dave Lewis, said the retailer had been working with all its suppliers to build a plan for each category. But he warned that fresh foods would be a “pinch point” if there was no deal because they could not be stockpiled.

With frozen and chilled warehouse storage space now fully booked, Tesco has taken an extra year’s lease on several hundred refrigerated containers, located in store car parks, which it usually has only at Christmas.

Morrisons

Stockpiled tins of Morrisons’ baked beans in the back of a car. Photograph: Redsnapper/Alamy

The Bradford-based supermarket chain has applied and been accepted for authorised economic operator (AEO) status which enables simplified customs procedures and the possibility of fast-tracked shipments for importers. Other retailers may have applied for this status, but have not confirmed the move and it is currently reported to be taking up to 12 months to obtain AEO approval from HMRC.

Majestic Wine

French vino at Majestic Wine. Photograph: Graham Turner/The Guardian

The wine merchants has stored 1m extra bottles of wine from France, Spain and Italy in case there are import problems or increases in duty post-Brexit.

Pets at Home

Pets at Home superstore in Stockport, Greater Manchester. Photograph: Christopher Thomond/The Guardian

The listed pet store has stockpiled £8m of extra supplies, including dog and cat food.

Sainsbury’s and Asda

A shopper walks past milk cartons in an aisle of Asda supermarket in London. Photograph: Neil Hall/Reuters

Both supermarkets signed a British Retail Consortium-backed letter calling on the government to avoid a no-deal Brexit. The letter said these companies were stockpiling but warned that retailers typically keep no more than two weeks’ inventory.

Food processors

Shopping basket containing Premier Foods products. Photograph: Premier Foods/PA

Premier Foods

The owner of Mr Kipling, Ambrosia and Sharwoods, has said it is spending £10m on Brexit preparations and has stockpiled both ingredients and its most popular products, such as Oxo cubes and Bisto gravy, to protect against port delays.

Mondelēz International

Cadbury chocolate sold at Easter. Photograph: Sam Frost/The Guardian

The company behind Cadbury chocolates has been stockpiling ingredients as well as finished chocolates and biscuits.

Ornua

WTO tariffs on cheddar are as high as 42%. Photograph: David Marsden/Getty Images

The Irish dairy company behind brands including Kerrygold and Pilgrims Choice, is stockpiling cheddar in the UK to ensure that its product can get to supermarket shelves and beat any shock price hike if the UK crashes out of the EU bloc on 29 March.

World Trade Organization tariffs on cheddar are as high as 42%, and Irish cheesemakers fear sales would plummet if they had to pass on the full extra cost to the consumer. Of the 200,000 tonnes of cheese made a year in Ireland, 45,000 tonnes is cheddar exported to the UK.

Unilever

Unilever product, Marmite. Photograph: Chris Radburn/PA

The Anglo-Dutch conglomerate has said it is stockpiling large supplies of Magnum ice-creams in the UK amid concerns about importing them from its factories in Italy and Germany. Unilever has also been building up stocks of materials to make and package products including aluminium, plastics and propellants.

Farmers

Lettuce pickers in Lancashire. Photograph: Alamy

Salad growers

In the spring, the vast majority of salads eaten in the UK are imported from southern Spain. Catering supplier Reynolds, has said it usually holds only 1.5 days of stock to ensure its product is fresh in stores. It is considering increasing its stocks on some products, such as tomatoes, but that is severely limited because its delicate products can deteriorate fast.

Andy Weir of Reynolds said the company has been investigating using suppliers in other countries, such as Morocco and alternative ports to Dover and Calais, through which most salads are currently shipped. He is also looking at flying in product.

However alternative ports add time and cost while flying in product is very costly. Weir has previously flown in lettuce from the US when bad weather in Spain hit supplies, but he said this was only a last resort.

Fruit farmers

Farmers fear uncertainty over EU workers’ rights. Photograph: Robert Harding Picture Library L/Alamy

The main concern for soft fruit farmers is securing enough people to pick produce amid uncertainty over EU workers’ right in the UK after 29 March. Harry Hall at Hall Hunter Partnership, the UK’s biggest berry grower based across several sites in southern England, said the company currently had a good supply of seasonal workers and was assuring them it wouldsupport any bureaucratic changes.

He said the company would also pay living and working conditions to encourage pickers to come. But he said a no-deal Brexit under which EU workers were excluded from the UK would be “armageddon”. “If that happens the whole country will come to a halt, forget the berries,” he said.