Why New Zealand is accused of propping up the illegal occupation of a west African nation.

It sounds improbable, but New Zealand has become embroiled in one of the world's longest-running refugee crises, on the other side of the world. For those who live in the refugee camps in Algeria, New Zealanders are inadvertently perpetuating this conflict. Charlie Mitchell reports in part two of Growing Pain, a Stuff series on our dangerous addiction to fertiliser.

There's only one television channel to watch in 'The Devil's Garden', the network of refugee camps in the Sahara Desert.

It usually shows news, 24 hours a day. In May last year, one story in particular dominated its coverage - one in which New Zealand was the antagonist.

At the other end of the continent, a ship called the Cherry Blossom, flagged to the Marshall Islands, had crept into Coega, a port on South Africa's eastern cape, to refuel. Before the ship could leave, it was locked down by authorities.

The Cherry Blossom had been heading to Tauranga in New Zealand. Ballance Agri-Nutrients had planned to buy its cargo, roughly 54,000 tonnes of phosphate rock with a value of around $7m. But Furness Withy, the company that chartered the ship - working from bland offices in London and Melbourne - had made a critical mistake.

Instead of going west, the ship was told to go east. As it left the occupied territory of Western Sahara, the ship was tracked by the Polisario Front, the Saharawis' political representatives, which act as a government in exile.

When the Polisario realised the ship had stopped in South Africa, it seized on a rare opportunity. Around 45 countries recognise the Saharawis as an independent nation, and one of them is South Africa.

The Polisario filed a court order claiming the ship contained stolen property which rightfully belonged to the Saharawi people.

The ship was anchored 4km off-shore, costing Furness Withy $10,300 a day while a court battle played out.

Three weeks later, a similar ploy happened in Panama. A phosphate-laden ship had been crossing the canal, bound for Canada, when it was detained by Panamanian authorities.

The case in Panama was dismissed, and the ship continued to Canada. Around the same time, a replacement ship arrived in Tauranga, while the Cherry Blossom remained tied up.

A couple of months later, the South African courts ruled the phosphate belonged to the Saharawis, and the cargo was seized and auctioned off. A buyer wasn't found - likely because Morocco had threatened legal action against any purchaser - so the cargo was ultimately bought by Furness Withy, which sold it back to the mine owner OCP for $1.

Almost exactly a year after it was detained, the ship left South Africa, and the whole phosphate trade had changed.

SUPPLIED The NM Cherry Blossom, which had been headed for Tauranga, was forced to anchor 4km off the South African coast, costing $10,300 a day.

The Saharawis have been waiting for the international system to find a solution to the crisis. A referendum among the Saharawis was promised in 1991, but still hasn't happened.

Critics of the occupation say the gridlock is largely due to Morocco, which would need to approve any referendum, but which benefits from the status quo.

Generations of Saharawis have been trapped in the desert, peacefully resisting the occupation of their homeland, with no progress.

It has led them to new methods - using the international legal system and appealing to corporate responsibility to make Morocco's occupation more trouble than it's worth.

The Cherry Blossom saga was a major victory for the Polisario. It caused a scene. And, if nothing else, it made it clear that in some parts of the world, Morocco's occupation is seen not just as unjustified, but illegal.

The Polisario has had success in other ways, too. In recent years it has been directly lobbying companies to stop trading in phosphate. The number of companies doing so has fallen from around 15 to three.

New Zealand, stubbornly, has continued to trade in phosphate, despite legal and reputational threats. While other global multinational companies bowed to ethical pressure from investors, the New Zealand companies are co-operatives, with no outside investors.

"The only two co-operatives involved in this entire sector, owned by the farmers of New Zealand, seem untouchable," says Erik Hagen of Western Sahara Resource Watch.

The Polisario has stressed it will continue its campaign, to shed the last buyers of the phosphate it claims as theirs.

Buoyed by its success in South Africa, it believes it has the law on its side.

"The Saharawi government tried for years to engage both companies in a conversation, and only very recently decided to rely on the law to assert what are well founded basic rights in the international legal order," says Kamal Fadel, a Polisario Front representative.

"We have made it clear to Ballance and Ravensdown that they will face legal action sooner or later should they persist in their wrong and illegal acts."

SAHARAWI CAMPAIGN AGAINST THE PLUNDER/SUPPLIED Saharawian refugees protest the involvement of New Zealand's fertiliser companies in the phosphate trade.

Pro-Saharawi groups, including the government in exile, believe New Zealand is actively hampering the peace process.

On the one hand, New Zealand argued for peace through the UN, but on the other, it has allowed trade to continue for its own economic well-being, funding the occupation.

"The trade provides Morocco with the necessary funds to purchase equipment and arms that are used to oppress our people and occupy our homeland," Fadel says.

"New Zealand companies have put money before morals. They are blinded by their desire to make profits so they ignore the facts that they are involved in an illegal, unethical and immoral trade."

It has led to anger within the camps. The Cherry Blossom incident made it well-known among Saharawis that New Zealand is the country buying the phosphate from their homeland.

For some, it has led to a cognitive dissonance: A country known for its respect for human rights is knowingly benefiting from what some Saharawis see as robbery.

"For many Saharawis, New Zealand is a democratic country where human rights and values are respected," says Jalihenna Mohamed, a Saharawi living in the camps who campaigns against the phosphate trade.

"But the involvement of New Zealand companies, Ballance and Ravensdown, has changed this image badly."

ARTURO RODRIGUEZ/AP Saharawis watch as Polisario soldiers blow up Moroccan landmines near a Western Saharan village.

Mohamed, like others, believes the trade in phosphate is "illegal and unethical".

The Saharawis are happy for the trade to continue, but it must be with them, the phosphate's rightful owners. New Zealand has become the major barrier to that, Mohamed says.

"We see these companies [Ballance and Ravensdown] as directly and intentionally involved in enlarging our suffering as oppressed people by ensuring the continuation of Morocco's illegal occupation of our land.

"The only way they fix this is to immediately stop importing our phosphate until we enjoy our right to self-determination and independence."

Ballance and Ravensdown source similar quantities of phosphate from Western Sahara, from the same mine. Both companies say the alternative sources are no better.

"When you look around, every source has some challenges," Ravensdown supply chain manager Mike Whitty says.

"The reality is with many of them, some are not options because the product is all consumed internally and further processed, but clearly there's a number of challenges as you go through where phosphate comes from - political issues, unrest, some countries putting quotas, taxes and other constraints on access."

Whitty says Ravensdown is keenly aware of the political situation in Western Sahara, but the company defers to the UN process.

TOUFIK DOUDOU/AP A Sahrawi woman walks through the Smara refugee camp near Tindouf in 2016.

Earlier this year, a delegation from the mine's owner, OCP, visited New Zealand.

The Moroccans landed in Auckland and drove to Tauranga, past the farms made green with phosphate from its mine, to meet with officials from Ballance, who nine months earlier had become embroiled in the dispute over the Cherry Blossom.

A few months later, the trip was done in reverse. Mark Wynne, Ballance's chief executive, flew to Western Sahara, west of the wall, to look at the mine.

This exchange has happened many times in the three decades New Zealand has bought phosphate from Western Sahara.

But the ongoing geopolitical conflict, and the rising pressure from opponents to the Moroccan regime, have made the situation more tenuous than ever.

The close bind between the companies has gone on for decades. OCP's Western Saharan mine supplies around 70 per cent of New Zealand's phosphate; the company's vice-president has said he hopes to keep supplying New Zealand with Western Saharan phosphate for 30 years.

For Morocco, which is sitting on most of the world's phosphate rock, the incentive to keep the mine is obvious.

If Western Sahara became independent, it would immediately become a major competitor. OCP already makes billions in profit each year from its mines, money which, in part, flows to the Moroccan king.

As other nations use up their internal supplies, they will have no choice but to buy from Morocco.

The value of the phosphate sent to New Zealand in 2016-2017 was an estimated $45m, which amounts to well over $1b over the expected life of the mine. It would have taken a hit when the other companies pulled out, but most importantly, Morocco has the control. It can maintain its monopoly and has a reason to keep the mine open.

Opponents believe that if New Zealand stopped buying from Bou Craa, it could become too costly for OCP to keep the mine open. It could push Morocco closer to the peace process, and ensure the Saharawis had phosphate left to trade should they return to their homeland as an independent nation.

"As long as Morocco can profit from its illegal presence in Western Sahara by exporting minerals from the territory to New Zealand, it sees no need to engage in the UN peace talks that the international community is asking for," Erik Hagen says.

"If the exports to the two companies [Ballance and Ravensdown] were stopped, it would mean that the minerals of Western Sahara would be accessible to its owners once the illegal and brutal occupation terminates.

"The phosphate rock is the resource that the people of Western Sahara is to build its own nation on."

* In part three of Growing Pain, a Stuff series, Charlie Mitchell explains the strange bind that keeps New Zealand companies returning for more phosphate from Western Sahara.