Fans of Mars bars had better hope that Theresa May secures a good trade deal with the EU or the price of the chocolate will rise sharply, a senior executive at the company has said.

A hard Brexit, where the UK ends up trading with the EU under World Trade Organisation rules, would mean 30 per cent tariffs imposed on confectionery imports.

This will inevitably be passed on to consumers and could threaten jobs, Fiona Dawson, global president of Mars Food, will say in a speech to the American Chambers of Commerce in Brussels on Friday.

Much of the debate around tariff increases has so far focused on financial services and the car industry, but Mars is attempting to highlight the importance of the food industry.

The company employs 3,800 workers in the UK and, like many other businesses in the food sector, relies on open borders as it uses supplies from all over the world and is packaged and sold in a variety of countries.

“The absence of hard borders with all their attendant tariff, customs and non-tariff barriers allows for this integrated supply chain, which helps keep costs down,” Ms Dawson will say.

“The return of those barriers would create higher costs, which would threaten that supply chain and the jobs that come with it,” Ms Dawson will say.

Prices of other foods could also face big price hikes without a friendly trade deal. Under WTO rules, animal products would be taxed 20 per cent, cereals more than 15 per cent and fish and fruit more than 10 per cent.

Significant new tariffs would also apply outside the food sector, notably in the area of clothing and textiles.

Prices of many famous brands have already risen as a result of the collapse in the value of the pound.

Mars campaigned for Britain to stay in the EU but now says focus must be concentrated on securing as free and open trade as possible after Brexit.

“There can be no economic advantage in either side restricting trade with a large market situated on its doorstep. In simple terms, if the UK and the EU fail to agree on a new preferential deal, it will be to the detriment of all,” Ms Dawson will say.

How Brexit affected Britain's favourite foods from Weetabix to Marmite Show all 8 1 /8 How Brexit affected Britain's favourite foods from Weetabix to Marmite How Brexit affected Britain's favourite foods from Weetabix to Marmite Weetabix Chief executive of Weetabix Giles Turrell has warned that the price of one of the nation’s favourite breakfast are likely to go up this year by low-single digits in percentage terms. Reuters How Brexit affected Britain's favourite foods from Weetabix to Marmite Nescafé The cost of a 100g jar of Nescafé Original at Sainsbury’s has gone up 40p from £2.75 to £3.15 – a 14 per cent rise—since the Brexit vote. PA How Brexit affected Britain's favourite foods from Weetabix to Marmite Freddo When contacted by The Independent this month, a Mondelez spokesperson declined to discuss specific brands but confirmed that there would be "selective" price increases across its range despite the American multi-national confectionery giant reporting profits of $548m (£450m) in its last three-month financial period. Mondelez, which bought Cadbury in 2010, said rising commodity costs combined with the slump in the value of the pound had made its products more expensive to make. Cadbury How Brexit affected Britain's favourite foods from Weetabix to Marmite Mr Kipling cakes Premier Foods, the maker of Mr Kipling and Bisto gravy, said that it was considering price rises on a case-by-case basis Reuters How Brexit affected Britain's favourite foods from Weetabix to Marmite Walkers Crisps Walkers, owned by US giant PepsiCo, said "the weakened value of the pound" is affecting the import cost of some of its materials. A Walkers spokesman told the Press Association that a 32g standard bag was set to increase from 50p to 55p, and the larger grab bag from 75p to 80p. Getty How Brexit affected Britain's favourite foods from Weetabix to Marmite Marmite Tesco removed Marmite and other Unilever household brand from its website last October, after the manufacturer tried to raise its prices by about 10 per cent owing to sterling’s slump. Tesco and Unilever resolved their argument, but the price of Marmite has increased in UK supermarkets with the grocer reporting a 250g jar of Marmite will now cost Morrisons’ customers £2.64 - an increase of 12.5 per cent. Rex How Brexit affected Britain's favourite foods from Weetabix to Marmite Toblerone Toblerone came under fire in November after it increased the space between the distinctive triangles of its bars. Mondelez International, the company which makes the product, said the change was made due to price rises in recent months. Pixabay How Brexit affected Britain's favourite foods from Weetabix to Marmite Maltesers Maltesers, billed as the “lighter way to enjoy chocolate”, have also shrunk in size. Mars, which owns the brand, has reduced its pouch weight by 15 per cent. Mars said rising costs mean it had to make the unenviable decision between increasing its prices or reducing the weight of its Malteser packs. iStockphoto

“Imposition of significant trade barriers would ultimately hurt everyone and undermine, rather than strengthen, European unity.“

Lib Dem MP Tom Brake said: "This shows the threat posed to living standards by a hard Brexit.

"People with a sweet tooth risk being left with a sour taste in their mouths because of this Government's reckless plans to leave the Single Market.

"There is already Brexit squeeze on living standards caused by the plunging pound and higher prices. Crashing out of the EU without a deal would mean more price hikes on some of Britain's favourite foods."

In January, Theresa May signalled she is willing to drag Britain through the hardest of Brexits, risking the loss of billions of pounds and plummeting GDP, if both Brussels and the UK’s Parliament fail to give her what she wants.

In an act of brinkmanship, the Prime Minister warned that “no deal for Britain is better than a bad deal for Britain”.