Beekeepers and their supporters have staged a demonstration in central London, urging Britain to support a ban on certain pesticides.
The 'March of the Beekeepers' in Parliament Square comes ahead of a crucial vote in Brussels next week.
Campaign groups are urging the Environment Secretary Owen Paterson not to block an EU proposal to suspend the use of certain types of neonicotinoid pesticides which they claim are linked to a decline in the bee population.
Member states are due to decide whether or not to introduce a two-year moratorium on their use on Monday.
Unlike France, Spain and Italy, Britain is widely expected to abstain or vote no against the neonicotinoid ban, saying the impact of the pesticides on bees is unclear and the restrictions could harm crop production.
Celebrities including fashion designers Dame Vivienne Westwood and Katharine Hamnett and artist Rachel Whiteread will be among those protesting at Westminster.
Ahead of the march, Ms Hamnett told Sky News: "The European Food Safety Agency - who are usually very right wing and on the side of business - are saying we definitely need this ban, and if they are saying it we really are in trouble.
"We have a huge problem with the British Government failing to support it and it's quite hard to understand when you have got the Pesticide Action Network, the Soil Association, the Beekeepers Association (and) all the scientists saying this group of pesticides, neonicotinoids, kills bees."
Friends of the Earth, one of the demonstration organisers, said the Government needed to take urgent action to protect declining bee populations by supporting the European Commission proposals.
The group's head of campaigns, Andrew Pendleton, said: "Ministers can't ignore the growing scientific evidence linking neonicotinoid insecticides to bee decline.
"Their claims to be concerned about bee health will ring hollow if they fail to back European moves to restrict the use of these chemicals.
"If we lose our bees and other vital pollinators it will have a devastating impact on our food, gardens and environment. We urgently need tougher pesticide restrictions and a British Bee Action Plan to tackle all the threats they face."
But others claim there is no evidence to suggest neonicotinoids do harm bees.
Nick von Westenholz, chief executive of the Crop Protection Association, which represents the pesticides industry, told Sky News that while laboratory tests had shown some impact, "out in the field there is no effect being shown on bee health in real life".
Chemical firm Syngenta added: "The groups marching today ... have never presented any evidence from the field that these pesticides damage the health of bees.
"Somewhat irresponsibly, they are presenting a ban on them as the silver bullet for improving bee health."
A spokesperson for the Department for Environment, Food and Rural Affairs (Defra) said: "We respect people's right to protest but decisions that affect the whole of Europe need to be based on scientific evidence. So far studies have not shown that neonicotinoids pose a serious threat.
"We have urged the EU to carry out a European-wide study before making a decision. Instead, it is pressing ahead with a ban that could have serious unintended consequences for food production.
"Unless the EU's proposals change we will have to vote against them."
Earlier this month a cross party committee of MPs, the Environment Audit Committee , unanimously urged the Government to restrict the use of sprays containing neonicotinoids.
The demonstration has been organised by nine campaign groups - Avaaz, Buglife, Environmental Justice Foundation, Friends of the Earth, Greenpeace, Pesticide Action Network UK, RSPB, Soil Association and 38 Degrees.