The first shipment of palm oil certified as environmentally sustainable by the Roundtable on Sustainable Palm Oil (RSPO) is on its way from the rainforests of Malaysia to the UK this week, where it will eventually end up on the shelves of Sainsbury's supermarkets.

Last year, the trade group launched a certification scheme designed to allow palm oil producers to prove their crops have come from legal and environmentally sustainable plantations that have not contributed to rainforest clearance.

The scheme has won significant support from both plantation operators and palm oil purchasers - including Tesco, Nestle, Sainsbury's and Unilever, all of which have signed up to join the RSPO - who have faced criticism from green groups for indirectly supporting illegal plantations that result in the destruction of rainforest in countries such as Indonesia and Malaysia.

Jan Kees Vis, president of the RSPO, hailed the first shipment of RSPO certified palm oil as "a small but significant step towards having all the world's palm oil produced in a socially and environmentally sustainable way".

However, environmental groups such as Greenpeace have taken issue with the rigour of the RSPO's sustainability criteria. The group produced a report last year which concluded that the RSPO standards will not prevent forest and peatland destruction, and accused a number of RSPO members of not taking sufficient action to limit the palm oil industry's environmental impacts.

"On-the-ground investigations by Greenpeace reveal that RSPO members are dependent on suppliers that are actively engaged in deforestation and the conversion of peatlands," the report said.

Belinda Fletcher, senior forests campaigner at Greenpeace, said the RSPO must improve the standards by which it judges sustainably-certified plantations if it wants to be taken seriously.

"Not only are the standards not tight enough, but they're not delivering on those standards," she said. "There has to be a halt on expansion into rainforests and peatland areas."

Greenpeace said that even if the RSPO does tighten its standards palm oil plantations will continue to contribute to rainforest destruction as RSPO members only account for around 40 per cent of global production.

A high profile campaign by the lobby group against Unilever, one of the largest buyers of palm oil, led to the company's recent endorsement of Greenpeace's calls for a moratorium on any further expansion of palm oil plantations into rainforest areas.

However, the RSPO has so far resisted similar calls to support the proposed moratorium.

Meanwhile, supermarket chain Sainsbury's defended its purchasing of RSPO-certified palm oil. "Any sustainability standard has to be dynamic and constantly challenged. But I'm confident that the palm oil we've bought is of a higher standard and doesn't compare with anything we have sourced before," said Fiona Wheatley, natural resources manager for the supermarket chain.