Orang-utans arrived for work at Unilever’s offices in London, Rotterdam and Rome last month, carrying piles of leaflets.

They left a few hours later but in that short time the costumed Greenpeace volunteers had put a dent in the global conglomerate’s claims to sustainability.

The protest was aimed at highlighting Unilever’s use of palm oil supplied by companies destroying the rainforests of Indonesia – home to the orang-utan – but also at what the organisation regards as a “greenwash”.

Tim Birch, a Greenpeace campaigner, said: “Unilever pretends to be a responsible company, but if they invested as much in sorting out their suppliers as they do on greenwashing their brand, they could fix this problem for good.”

Greenwashing is an accusation now regularly levelled at big businesses. Lord Smith, chairman of the Advertising Standards Authority (ASA), reported earlier this year that complaints about companies who made green claims had risen from 117 in 2006 to 561 in 2007. “What we are seeing are claims about being carbon neutral, zero-carbon emissions and use of words such as ‘sustainable’, ‘organic’, ‘100% recycled’ or ‘greenest car in its class’. Many of these claims are exaggerated or misleading,” he said.

The ASA is planning an industry summit next month, at which environmentalists, advertising agencies and companies will consider new guidelines on what is acceptable.

A recent survey by McKinsey, the global management consultancy, found that consumers were becoming increasingly cynical. Sheila Bonini, of McKinsey, said: “These issues are . . . regarded by almost half of survey respondents as an area in which corporations have a negative impact on society because they pollute and otherwise damage global ecosystems.”

Such attitudes suggest that the repercussions for companies that use the black arts of public relations to try to generate an undeservedly good reputation could be serious indeed. But Solitaire Townsend, chief executive of Futerra (www.futerra.co.uk), a consultancy that publishes The Greenwash Guide, believes consumers could become so sceptical that they abandon sustainable products.

“Greenwash means confidence in green advertising is at an all-time low, with only 10% of consumers trusting information from business and government. If they can’t believe the claims then they won’t buy the products and the good will lose along with the bad.

“Greenwash is the spanner in the works that could sabotage the whole environmental movement within business,” Townsend says.