It is one of the few British supermarket staples to have bucked the trend during the cost-of-living crisis, with the price of a bunch of bananas no more expensive today than three decades ago. Every country in the world with lower prices than the UK has its producers of the fruit.

The Government has now been accused of pursuing an irresponsible post-Brexit policy that could reduce the price of bananas further in the shops – but at the cost of the livelihoods of thousands of workers on small plantations in some of Africa's poorest countries.

The British market is already dominated by the so-called "dollar banana" producers of Latin America who can sell cheaply, having benefited from rolled-over EU-negotiated free trade deals that have cut the import taxes, or tariffs, on the fruit.

The EU, however, promised in 2019 not to cut tariffs imposed on the big producers any further in recognition of the impact on the smaller African competitors. The UK's exit has freed it from that pledge to the world's poorest.

According to Afruibana, the Pan-African association of banana producers and exporters, all the indications are that the result will be betrayal, with the UK government ditching the EU promise to protect them.

Banana tariff concessions have already been made in the last year to Mexico and Peru as part of the UK's accession to the Comprehensive and Progressive Trans-Pacific Partnership (CPTPP). A trade deal with Australia will see all tariffs lifted within eight years.

The UK government is now engaging in a specific banana tariff review as part of its trade deal with the Andean countries – Colombia, Ecuador and Peru – which the African producers say could wipe out businesses in Ghana, Cameroon and Ivory Coast, countries whose economies are among the least diversified in the world.

The foreign secretary, James Cleverly, has refused to commit the UK to the EU pledge.

Joseph Owona Kono, the president of Afruibana, said: "Afruibana was deeply concerned to see the UK lower banana tariffs for Peru and Mexico as part of its accession to the trans-pacific trade agreement with no consultation with African governments. We are worried that this could signal a departure from the UK's vital and longstanding commitment to support and develop our sector.

"If similar concessions are made in forthcoming negotiations with the UK's already dominant suppliers such as Ecuador, Colombia or Costa Rica, this would lead to less choice for British consumers and will put the livelihoods of thousands of workers, their families and supporting businesses across the African banana sector in grave danger."

The highly competitive supermarket sector in the UK, with the decades of price wars during which brands competed for footfall by heavily discounting bananas, has been a significant factor behind the low banana prices enjoyed by British consumers along with the rollover of free trade agreements signed with the EU when the UK was a member state. The ten major retail brands in the UK sell 90% of the bananas.

Latin American suppliers dominate, with the three top suppliers – Colombia, Costa Rica and Ecuador – accounting for 62.7% of the market.

The 11.5% of the market held by African nations is said by Afruibana to provide more than 80,000 direct and indirect high-quality jobs and to sustain about half a million people in rural areas.

The African producers claim the move to cut costs for Latin American producers will not necessarily lower prices further for the British shopper but will instead be pocketed farther up the line as the cost to the consumer is already so low.

Gareth Thomas, a shadow trade minister, said the disregard for the producers in Africa followed a trend of signing deals without an understanding of the broader repercussions.

He said: "Sadly it isn't surprising that ministers might undermine the prospects of the poorest and particularly those in a key Commonwealth ally. Ministers have given little attention to Africa, having axed the Department for International Development and cut aid funding. This is yet another example of a trade deal Liz Truss and Greg Hands signed without thinking through the long-term implications."

The Windward Islands' smallholder banana industry has already fallen by the wayside amid tariff cuts for others. In 2012, the UK imported 12,146 tonnes from the 30,000 banana farmers on the island of Saint Lucia. By 2022, this had declined by 95% to just 541 tonnes.

A Department for Business and Trade spokesperson said: "The UK is using our trade strategy to support developing countries' economies, while also backing British business and helping consumers. Last year we launched a new developing countries trading scheme to make it better for developing countries to export to the UK and 99% of goods imported from Africa will enter the UK duty free – reducing costs for shoppers at the checkout."

Supermarket staples that have bucked the trend to stay cheap

Bananas per kilo: 115p in September 1990 and today 115p

Cucumbers: 60p in September 1990 and today 83p

Oranges per kilo: 21p in September 1990 and today 43p

Carrots per kilo: 57p in September 1990 and today 66p