The plutocrats of palm oil are in trouble. The makers of Wall's ice cream and Dove soap and Flora margarine are worried you'll get the idea that these products are being produced at the expense of the rainforests of southeast Asia. Because they are. And, so far, efforts to rebrand palm-oil plantations as oases of sustainability have proved about as convincing as those old ads that insisted you couldn't tell the difference between butter and margarine.

In late November, the Roundtable on Sustainable Palm Oil (RSPO) will hold its sixth annual meeting in on the Indonesian island of Bali. Food manufacturers, commodity traders and plantation owners will applaud the "first trickle" of palm oil certified as wildlife and climate-friendly and definitely not grown on recently deforested land.

Sadly, this will underline how, after six years of trying to identify sustainable sources of palm oil, the RSPO has to admit that 99% of the ubiquitous edible oil – found in a third of all the products on supermarket shelves – cannot be shown to have been produced sustainability.

In the chair in Bali will be Unilever's director of sustainable agriculture, Jan Kees Vis. The Anglo-Dutch conglomerate Unilever (purveyors of the Wall's, Dove and Flora brands) began life as Lever Brothers, obliterating the forests of west Africa a century ago to create palm oil plantations. Today, it buys more than a million tonnes of the oil annually from deforested Malaysia and Indonesia.

The world is getting in a fuss about growing palm oil for biofuels. But the vast majority of the crop – more than 80% of which comes from these two countries – goes into foodstuffs and soap products. Rainforests are being burned and felled across the islands of Borneo and Sumatra to create new land for palm-oil plantations.

Fearing a backlash from consumers, Unilever was one of the founders of Roundtable. But six years on, that body is being dismissed as a front for continuation of business as usual in the jungle clearings. Earlier this year, about 200 environment and human rights groups signed an "international declaration against the greenwashing of palm oil by the RSPO".

And one of Unilever's leading suppliers has been singled out. The Singapore-based Wilmar International has a huge land bank across Indonesia waiting to be cleared and planted with palm oil. Wilmar was recently forced to concede defeat in a long dispute with Friends of the Earth over whether it was linked to illegal land clearing for palm oil.

Unilever insists that it is sincere. Some other food manufacturers are seeking alternatives to palm oil. But Unilever promises instead that by 2015 all its palm oil will come from sustainable plantations. Leading retailers such as Sainsbury's make similar promises. Last November, Sainsbury's announced that it was "switching to sustainable palm oil" in its own-brand food. Critics say such promises are pie in the sky. At Sainsbury's, a year after that bold promise, just one brand of fish fingers has switched.

Progress seems bound to be slow while most of the producers of palm oil remain in denial about their problems. The Malaysian Palm Oil Council is haughtily dismissive of any suggestion that the methods of its members may be less than perfect – claiming that they only plant on land zoned for agriculture.

But that provides little comfort for conservationists. Particularly in Sarawak, the Malaysian province on Borneo, large amounts of forest land is zoned for agriculture, and the state is aggressively promoting conversion. Researchers say active deforestation is still creating space for palm oil.

Nonetheless, the Malaysian council's boss, Yusof Basiron, tells anyone who will listen that the RSPO, of which the council is a prominent member, is merely a promotional tool. Its system of certification is a "condition imposed by certain markets to certify practices that Malaysian planters have been undertaking for years." Such statements appear to breach the RSPO's own rules which forbid "claiming conformity to RSPO principles and criteria" without formal certification.

Can the likes of Unilever and Sainsbury's get all their palm oil from "sustainable sources" by 2015 as they promise? In one sense, maybe. Cynics point out that rainforest scientists expect both Borneo and Sumatra to be virtually treeless by then. There will be no more to chop down, so palm oil plantations will no longer be accused for deforestation.

But meanwhile, the patina of sustainability being wrapped round our biscuits and soap and ice cream and margarine and cosmetics and much else is helping fuel their final destruction.