If you ate a corn on the cob, green beans or some spring onions in the UK this winter, chances are it would have come from one of two farms at the edge of the Sahara, in the north of Senegal.

The West African nation is becoming an important player in the UK's food supply. Is that a good thing?

Hidden behind green leaves and thick stalks you can hear Diarra at work before you see her.

The cobs of corn she's harvesting are so abundant and the plants so tall, she's almost lost in a sea of maize. And the job at hand is tough.

This far north in Senegal, so close to the desert, temperatures can exceed 35C at this time of the year, and there's little or no rainfall.

Working at speed and with sunhats on, Diarra and her team of pickers make a steady sound of rustling, followed by a thud-thud, as they strip the cobs off each plant and place them in soft buckets strapped to their backs.

Within an hour, the cobs will be inside a refrigerated pack-house and chilled down to 0C. Soon after, they'll be driven by truck to a port near the capital, Dakar, and loaded onto a container ship. Six days later, they'll be on sale inside a British supermarket.

Diarra is one of 9,000 employees, mostly women, working on two British-run farms in Senegal's Saint-Louis region.

Between January and March, if you browse the fresh produce aisles of the UK's biggest food retailers, including Tesco, Sainsbury's, Asda, Aldi and Lidl, you're likely to see spring onions, radishes, green beans, chillis, butternut squash, and cobs of corn, all labelled Produce of Senegal.

The hot climate and sandy, parched soil make this an unlikely place for fruit and vegetables – or so you might think.

And yet, it's from here, at the edge of the desert, two of the UK's biggest fresh produce businesses - G's Fresh and Barfoots - are growing an increasing amount of food.

The origins of the farms go back to the early 2000s. Back then, French entrepreneur and agronomist Michael Laurent began using Google Earth to identify new locations for food production.

Saint-Louis, he realised, has an abundance of sunlight, land and labour. And, although there is little rainfall, the 1,600km (1,000-mile) long Senegal River forms its northern border with the neighbouring country of Mauritania, before emptying into the Atlantic.

Some of this river water is diverted into a maze of canals. A network of pumps and pipes then distributes the water across miles of arid land to irrigate the farms that have helped to green the desert.

"There was nothing here when we started," says Laurent. "It was all bush." Now the farms cover 2,000 hectares of the land, the equivalent of almost 3,000 football pitches.

On 500 of these hectares, salad specialist, Cambridgeshire-based G's Fresh, runs its Senegalese subsidiary, West African Farms.

Each week, during the British winter, it supplies two million bunches of spring onions, 100 tonnes of green beans and 80 tonnes of radishes. Some 70% is sold to UK supermarkets, the rest goes to retailers in Germany and the Netherlands.

The larger farm is a joint venture between Sussex-based Barfoots and SCL, the business founded by Michael Laurent.

This supplies the UK with 55 million cobs of corn each year, along with chillis, butternut squash, and also green beans.

The harvested vegetables go by road to the deep-water Port of Dakar five hours away by road. From there, one day a week, a large container ship departs on the 3,000-mile journey to Poole in Dorset.

The UK imports around 40% of its food, but for fresh produce during the winter the proportion of imports can be as high as 90%.

Until recently, the bulk of the UK's imports of fruit and vegetables came from southern Europe and Latin American countries such as Peru, while airfreighted produce, including green beans, came from East Africa.

West Africa is like the new kid on the block. Several factors are driving this, says Mike Knowles, an analyst specialising in fresh produce.

"Competition for land around the Mediterranean has become more intense, droughts in Spain have become more frequent, and flying vegetables across continents has fallen out of favour," he explains.

Also, as Brexit took away some of the advantages of importing food from continental Europe, Senegal became increasingly more appealing.

Politically and economically, the country is relatively stable. It's the only nation in West Africa which hasn't experienced a military coup or seen its government overthrown.

Overseas businesses aren't allowed to buy land, but it is possible to arrange long-term leases through agreements with the government and communities. Access to water is bought under licence though local management committees.

"We've been confident enough to invest around £70m in our Senegalese operation," says Julian Marks, group manager of Barfoot's.

And there's constant pressure for them to expand. "British consumers expect to be able to buy the same types of produce all year round," he says.

Senegal helps fulfil this demand, but what's in it for the African nation?

The 9,000 jobs created so far across the two farms is significant. Unemployment among Senegal's 18 million population grew during the pandemic and has remained high, hovering around 19%, with young adults in rural areas most affected.

Senegalese land rights activist Elhadj "Ardo" Samba Sow used to see the arrival of the foreign-owned farms as a form of neo-colonialism. Now working in local politics, he's more positive about their presence, "even if the jobs aren't so well paid".

The majority of the workers employed on the farms are guaranteed the minimum wage for agricultural workers in Senegal of around 2,500 West African francs a day ($4.50; £3). Pickers such as Diarra receive bonus payments if they're fast and exceed daily targets.

While Senegal has recently seen a rise in its minimum wage, Micheal Laurent acknowledges that wages are "not a lot", but that "profit margins are very low, and we need to remain competitive".

The low wages are another reason why the farms in Senegal could see further expansion.

"When we grow spring onions in the UK, 60% of the cost is labour," says Derek Wilkinson, managing director at G's Fresh. "In Senegal, labour counts for less than one third."

Even factoring in the cost of transportation from West Africa, on current trends Wilkinson believes it will soon make economic sense to replace more UK production with imports from Senegal, even during the British peak summer growing season. "It'll be down to the consumer to decide if they want to buy British or imported."

But is it a good thing to ship vegetables all the way to the UK from Senegal. "No," says Tim Lang, emeritus professor at City University, who first coined the term "food miles".

While transporting food by sea comes at a lower environmental cost than air freight, maritime shipping accounts for 3% of global greenhouse emissions.

"We should align our diets with the seasons as much as possible," says Lang, "And instead of imports from Africa, we need to be exploring the wider range of crops that can be grown in the UK."

Additional reporting from Jack Thompson

Read more global business stories