Even in the first light of dawn in the Tripa swamp forest of Sumatra it is clear that something is terribly wrong. Where there should be lush foliage stretching away towards the horizon, there are only the skeletons of trees. Smoke drifts across a scene of devastation.

Tripa is part of the Leuser Ecosystem, one of the world's most ecologically important rainforests and once home to its densest population of Sumatran orangutans.

As recently as 1990, there were 60,000 hectares of swamp forest in Tripa: now just 10,000 remain, the rest grubbed up to make way for palm oil plantations servicing the needs of some of the world's biggest brands. Over the same period, the population of 2,000 orangutans has dwindled to just 200.

In the face of international protests, Indonesia banned any fresh felling of forests two years ago, but battles continue in the courts over existing plantation concessions.

Here, on the edge of one of the remaining stands of forest, it is clear that the destruction is continuing.

Deep trenches have been driven through the peat, draining away the water, killing the trees, which have been burnt and bulldozed. The smell of wood smoke is everywhere. But of the orangutans who once lived here, there is not a trace.

This is the tough physical landscape in which environmental campaigners fighting to save the last of the orangutans are taking on the plantation companies, trying to keep track of what is happening on the ground so that they can intervene to rescue apes stranded by the destruction.

But physically entering the plantations is dangerous and often impractical; where the water has not been drained away, the ground is a swamp, inhabited by crocodiles. Where canals have been cut to drain away the water, the dried peat is thick and crumbly and it is easy to sink up to the knees. Walking even short distances away from the roads is physically draining and the network of wide canals has to be bridged with logs. The plantations do not welcome visitors and the Observer had to evade security guards to gain entrance.

To overcome these problems, campaigners have turned to a technology that has become controversial for its military usage but that in this case could help to save the orangutans and their forest: drones.

Graham Usher, from the Sumatran Orangutan Conservation Programme, produces a large flight case and starts to unpack his prized possession, a polystyrene Raptor aircraft with a two-metre wingspan and cameras facing forward and down.

The £2,000 drone can fly for more than half an hour over a range of 30-40km, controlled by a computer, recording the extent of the destruction of the forest.

"The main use of it is to get real time data on forest loss and confirm what's going on with fires," he says.

Habitats under threat. Photograph: Observer

They can also use the drone to track animals that have been fitted with radio collars. Graham opens his computer and clicks on a video. Immediately, the screen fills with an aerial view of forest, then a cleared patch of land and then new plantation as the drone passes overhead. "We are getting very powerful images of what is going on in the field," he says.

The footage is helping them to establish where new burning is taking place and which plantations are potentially breaking the law. Areas of forest where the peat is deeper than three metres should be protected – the peat is a carbon trap – but in practice many plantations do not measure the depth.

"They shouldn't be developing it but the power of commerce and capital subverts all legislation in this country. There is no law enforcement or rule of law," says Usher.

The battle to save the orangutans is not helped by the readiness of multinational corporations to use palm oil from unverified sources. Hundreds of products on UK supermarket shelves are made with palm oil or its derivatives sourced from plantations on land that was once home to Sumatran orangutans.

Environmental campaigners say that the complex nature of the palm oil supply chain makes it uniquely difficult for companies to ensure that the oil they use has been produced ethically and sustainably.

"One of the big issues is that we simply don't know where the palm oil used in products on UK supermarket shelves comes from. It may well be that it came from Tripa," says Usher.

In October, the Rainforest Foundation UK singled out Superdrug and Procter and Gamble (particularly its Head and Shoulders, Pantene and Herbal Essences hair products) for criticism over the use of unsustainable palm oil. A traffic light system produced using the companies' responses to questions from the Ethical Consumer group also placed Imperial Leather, Original Source and Estée Lauder hair products in the red-light category.

A separate report by Greenpeace, also issued in October into Sumatran palm oil production, accused Procter and Gamble and Mondelez International (formerly Kraft) of using "dirty" palm oil. The group called on the brands to recognise the environmental cost of "irresponsible palm oil production". According to the Rainforest Foundation's executive director, Simon Counsell, part of the problem is that even companies that do sign up to ethical schemes, such as the Roundtable on Sustainable Palm Oil, cannot be certain that all the oil they receive is ethically produced because of the way oil from different plantations is mixed at processing plants.

"The smaller companies sell to bigger companies and it all gets mixed. Even those companies making some effort cannot be certain that what they are getting is what they have paid for," he said.

Driving out of Tripa, the whole area appears to have been given over to palm oil plantations; some long-established, 20-25ft tall trees in regimented rows, others recently planted. Every now and again there is a digger, driving a new road into what little forest remains, the first stage of the process that will end with the forest burned and gone and replaced with young oil palms.

There is a steady flow of lorries loaded with palm fruits, heading for the processing plant not far from the town of Meulaboh. From there, tankers take the oil to the city of Medan for shipping onwards.

It is outside Medan that the orangutan victims of clearances are taken to recover, at the SOCP's quarantine centre. These are the animals rescued from isolated stands of forest or from captivity. Those that can be will eventually be released back into another part of the island.

Anto, a local orangutan expert, says the spread of the plantations is fragmenting the remaining forest and isolating the orangutans.

"Then people are poaching the orangutans because it is easy to catch them," he says. "People isolate them in a tree and then they cut the tree or they make the orangutan so afraid that it climbs down and is caught. After that they can kill it and sometimes eat it. Or they can trade it."

This is what happened to Gokong Puntung and his mother. The one-year-old ape – now recovering with the help of SOCP – was rescued from Sidojadi village in February. He had been captured a month earlier in the Tripa forest.

A group of fishermen spotted Gokong Puntung and his mother trapped in a single tree and unable to reach the rest of the forest without coming down. The men apparently decided to try to grab the baby in the hope of selling it. One climbed the tree, forcing the mother to fall to the ground, where another man set about her and beat her with a length of timber. In the confusion, mother and baby became separated and the fishermen were able to get away. They sold the animal for less than £6 to a plantation worker.

"We got information from people who heard an orangutan crying in one house," says SOCP vet Yenny Saraswati. "They went in the house and found the baby orangutan in a chicken cage. The owner said he had bought it from people who had taken it from the plantation."

It was a very unusual case: more often, the mother is killed.

"They are very good mothers – better than humans," she says. "A lot of human mothers don't care for their babies, but I have never seen an orangutan leave its baby. They always hug them and don't let them cry."

That's why poachers tend to kill the mothers, says Anto. "They hit it with sticks. One person uses a forked stick to hold its head and the others hit it and beat it to death. But the young orangutans they sell."

The effect on Tripa's orangutans has been disastrous. Cut off from the population on the rest of the island, they teeter on the brink of viability; experts say they really need a population of about 250 to survive long term and, because orangutans produce offspring only once every six or seven years, it takes a long time to replenish a depleted population.

Those that remain in the forest face other dangers. Some die when the forest is burned, others starve to death as their food supply is destroyed.

If the orangutans did not already have it tough, there may yet be worse to come: gold has been found in Aceh's remaining forests and mining is starting.

"If there is no government effort to protect the remaining area, we will never know the orangutans here again," says Anto.

"If this continues they will be gone within 10 years."

In response to the criticism over its use of unsustainable palm oil, Superdrug said it "is aware of the complex issues surrounding palm oil and its derivatives, which are currently used in some of its own-brand products, and is committed to working with its suppliers to use sustainable alternatives when they become widely available."

Estée Lauder Companies, which makes Aveda hair products, said: "We share the concern about the potential environmental effects of palm oil plantations, including deforestation and the destruction of biodiversity and habitats."

The statement said that its palm oil (made from the pulped fruit) came from sustainable sources. But the company said the majority of its brands used palm kernel oil (from the crushed palm fruit kernels) and that it was working to develop sustainable supplies.

"We are committed to acting responsibly and will continue to work with our suppliers to find the best ways to encourage and support the development of sustainable palm kernel oil sources."

PZ Cussons, which makes Original Source and Imperial Leather products, along with the Sanctuary SPA range, said it was committed to using raw materials from sustainable and environmentally friendly sources wherever possible.

The company said it had "embarked on a sustainability journey" and was working with other producers to gain a better understanding of the supply chain and "to promote the growth and use of sustainable oil palm products". Mondelez International (formerly Kraft) said it wanted to eliminate unethical plantations from its supply chain by 2020.

"We fully share concerns about the environmental impacts of palm oil production, including deforestation. As a final buyer, engaging our supply chain is the most meaningful action we can take to ensure palm oil is grown sustainably," said a spokesman.

"Palm oil should be produced on legally held land, protecting tropical forests and peat land, respecting human rights, including land rights, and without forced or child labour.

"We expect palm oil suppliers to provide us transparency on the proportion of their supplies traceable to plantations meeting these principles by the end of 2013 and to eliminate supplies that do not meet these criteria by 2020."

Procter & Gamble, which makes Head and Shoulders, Herbal Essences and Pantene products, said it was "strongly opposed to irresponsible deforestation practices and our position on the sustainable sourcing of palm oil is consistent with our corporate sustainability principles and guidelines.

"We are committed to the sustainable sourcing of palm oil and have set a public target that, by 2015, we will only purchase palm oil from sources where sustainable and responsible production has been confirmed."