Syngenta, based in Basel, Switzerland, last year clocked up £7.3 billion worth of sales in more than 90 countries. Among the products it markets to farmers are insecticides which have been blamed for harming honeybees.

It now also co-funds a £1m project in the UK, announced last week, to research the decline of the bees. But the company has dismissed criticisms of its role in the project as “perverse”.

A film due to open in cinemas this week highlights the global plight of the honeybee and argues that insecticides are partly to blame. Called Vanishing Of The Bees, it is backed by the Co-operative retail group, which has a strict policy on the use of pesticides on the fruit and vegetables it sells, including a total ban on the use of several chemicals.

According to beekeepers, honeybee populations in the UK crashed by nearly a third in 2008. The implications are alarming, as bees contribute £200m a year to the UK economy, pollinating a third of our food.

Scientists speculate that a combination of factors may be involved, including disease, mites, weather and modern farming practices. But some argue that a group of widely-used nicotine-based insecticides known as neonicotinoids could be inflicting neural damage on bees, and contributing to their demise. Syngenta sells two products containing neonicotinoids, Actara and Cruiser.

To protect bee populations, some such insecticides have been banned or restricted in France, Germany, Italy and Slovenia. But they can still be used in other countries, including the UK and the United States.

A coalition of environmental groups has launched a campaign for a ban on neonicotinoids in the UK. The group includes the Soil Association, which certifies organic food.

Its Scottish director, Hugh Raven, said Syngenta had made its position clear by opposing a ban on neonicotinoids.

“The taint of commercial interest has undermined this research before it’s even started,” he said.

The research is also supported by the government’s Biotechnology and Biological Sciences Research Council. “The BBSRC should think again, and get a co-funder without this howling conflict of interest,” said Raven.

Professor Andrew Watterson, head of the occupational and environmental health research group at Stirling University, agreed there were “potential conflicts of interest in the project which may affect the credibility of the findings”.

Graham White, a beekeeper in the Scottish Borders and an environmental author, was scathing about Syngenta’s role: “Putting Syngenta in charge of UK research into the causes of honeybee deaths is arguably the equivalent of putting the tobacco companies in charge of research into lung cancer.”

But Andrew Coker, Syngenta’s head of corporate affairs in the UK, said: “It seems perverse that we put our money into researching bee health and then get criticised for it.”

Dr Celia Caulcott, BBSRC’s director of innovation and skills, also defended the research. She said: “The use of insecticides in agriculture is just one possible reason for the problems bees are facing. The most important thing to do right now is to understand what is happening and then translate that knowledge into actions to address the decline.”