Luxury coffee sold from the home of Labour leadership frontrunner Jeremy Corbyn is produced by poverty-stricken Mexican farmers, some of whom have earned less than the country’s minimum wage, The Mail on Sunday can reveal.

Laura Alvarez, the politician’s third wife, runs a business selling organic beans, and boasts that those who make it are paid ‘a fair wage and enjoy good conditions of employment’.

But this newspaper has discovered that Café Mam is produced by farmers in Mexico’s poorest state, who earn just 93p for each 500g bag that Ms Alvarez sells for £10.

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Laura Alvarez (left), Jeremy Corbyn's third wife, runs a business selling coffee beans produced by poverty-stricken Mexican farmers

Café Mam is produced by farmers (pictured) in Mexico’s poorest state, who earn just 93p for each 500g bag that Ms Alvarez sells for £10

Workers take turns to sleep in their factory (pictured) to stop thieves stealing the machinery and wrecking their livelihood

Our investigation found:

One farmer took home the equivalent of just £260 in a year after paying his workers – a quarter of the regional minimum wage;

A woman gets up at 4am each day to begin her back-breaking work, and wept when she was told how much her coffee is sold for by wealthy Westerners, including Mr Corbyn’s wife;

Itinerant workers are being paid between 80 and 130 pesos – £3.15 to £5.10 – a day to pick coffee;

Workers are living in tiny shacks with their families. They also had to take turns to sleep in their factory to stop thieves stealing the machinery and wrecking their livelihood.

The case has striking similarities to this newspaper’s revelations about the £45 feminist T-shirts sported by Labour’s last leader Ed Miliband, which turned out to be made by female workers paid just 62p an hour in an Indian Ocean ‘sweatshop’.

One tearful farmer urged Mr Corbyn’s wife last night: ‘Please think about us farmers and how we are struggling when people are making so much money off our hard work.’

Miss Alvarez, 46, who was born in Mexico, is the third wife of Mr Corbyn, the 66-year-old MP for Islington North, the shock favourite to become the next leader of the Opposition after thousands of union members who share his hard-Left views signed up to vote.

Workers - who are paid the equivalent of between £3.15 and £5.10 a day - are living in tiny shacks (pictured) with their families

Losing out: Farmers, including Roman Lopez Mejia (left), made as little as £260 last year

Last night, a spokeswoman for Miss Alvarez said: ‘Miss Alvarez is shocked to learn of The Mail on Sunday’s revelations. She has supported Café Mam in good faith and with due diligence and has accepted their Fair Trade certification. She has wanted to help people in her home country who are in desperate need.’

For the past two years, Miss Alvarez has been the sole director of Mexica Products Ltd, whose registered address is the couple’s home in Finsbury Park, North London. It is estimated to be worth more than £600,000.

Working as a Café Mam distributor, Miss Alvarez sells 250g bags of coffee for £5 and 500g bags for £10. Her website says it is ‘true artisanal Mexican coffee’ made ‘with passion and dedication from the co-operatives and small family producers’.

A section headed ‘We care about you’ boasts that Café Mam, made by a co-operative of 669 farmers in the highlands of southern Mexico and Guatemala, is certified organic. It claims: ‘All the members of a family, together with workers who receive a fair wage and who enjoy good conditions of employment, help to produce the coffee.

‘The purpose of Café Mam is to provide a livelihood for indigenous peasants and farmers in Chiapas, traditionally one of the most socially divided areas in southern Mexico.’

Café Mam’s own site claims: ‘Farmers receive a fair price for their harvest. In turn, they are able to stay on their land, keep their children in school, build health clinics, and make improvements to their land and farming equipment.’

But this newspaper found a very different picture when it visited Chiapas last week. The Mail on Sunday spoke to farmer Roman Mejia, 45, who was paid just 15,000 pesos – £600 – for his coffee beans last year. After he paid his workers and his costs he was left with just £260, a fraction of Mexico’s regional minimum wage, which equates to £852, and below the poverty line that is set at £775. Mr Mejia’s wife, daughter, two sons and a grandson all live with him in a 24ft by 18ft rainforest home.

Corbyn, the 66-year-old MP for Islington North, is the shock favourite to become the next Labour leader

Miss Alvarez, who runs Cafe Mam (logo pictured), said she was 'shocked' to learn of the allegations

One explanation for some farmers low income may be their low yield. Recently Mejia’s farm in Siltepec was devastated, like many farmers’, by a fungus and he lost half of his produce.

On the ranch of Heriberto Ventura in El Tarral, he told how he had lost money on this year’s produce, for which he was paid £2,400, and has had to take out bank loans. He lives with his wife and son in a small home with a tin roof.

Headquarters: The London home of Laura Alvarez and Corbyn

The 58-year-old said: ‘This year things were so bad we made a loss. I have to get loans from the bank. Sometimes they refuse, so I sell coffee beans to people on the side.’

Despite the claims made about the farmers’ living conditions by Café Mam’s website, many children have a 90-minute journey to school and if farmers or their families get ill, many of them face a three-hour trek to the nearest health centre.

Lucas Vellazquez Bartolon, 58, owns an 2.5-acre farm that supplies coffee to Café Mam. Last year he received £1,600. ‘Some years the money we get is so low but the price it is sold for in England never goes down. Sometimes we can’t afford food. But what can we do, we have no choice.’

Mother of six Idolina Sanchez Gonzalez, 53, fought back tears as she talked about her back-breaking work as a farm owner in the mountain village of La Victoria. She was paid £1,600 for her coffee last year, £800 of which went to her workers.

She said: ‘I get up at 4am and walk to the farm to start at 6am. I work until 4pm, sometimes later. We are only paid once, so it has to last all year and we have to work other jobs to pay our workers.’

Mam coffee – named after an ancient Mayan community – is grown high in the mountains at altitudes ranging from 3,900ft to 5,570ft above sea level. Once it is harvested the co-op leaders negotiate a deal with its client Royal Blue Organics, in Portland, Oregon.

The price agreed is based on the New York stock exchange, and is topped up to meet Fair Trade standards. Last year that was $176 per 60kg sack, equivalent to farmers earning just 93p for each 500g bag that Ms Alvarez sells for £10.