One of the worst ever incidents of mass poisoning of wild bees in the UK has come to light - approaching 500 bumblebee queens were found dead and dying on the outskirts of London.

The incident occurred in Havering, East London, next to a field of Oil seed rape that is thought to have been planted with imidacloprid treated seeds in autumn 2013. The bees were discovered in April by Sheila Horne who informed local naturalist Tony Gunton. They were shocked to discover hundreds of dead and dying bumblebees scattered all over public ground next to the flowering rape and along a nearby path. Tony identified the bees as being queens from at least three species.

Results of tests by the government science agency Fera have just been made public, they show that the bumblebees were contaminated with high levels (c.6 ppb) of the neonicotinoid imidacloprid, a partially banned neonicotinoid insecticide, and by two types of fungicide, including flusilazole - which will be completely banned in October 2014 due to its toxicity to fish.

Studies have shown that some fungicides are capable of greatly magnifying the toxicity of neonicotinoids to bees and this may have contributed to the scale of the slaughter.

"Hacton Parkway is usually a bumblebee haven, rough grassland with bramble patches - prime nesting territory, and it was heart breaking to discover a whole generation of queens wiped out like this. It only came to light because of Sheila's alertness - how many more bees have died unnoticed across the countryside? It's no wonder that pollinator populations are in decline" said Tony Gunton.

"This is a timely reminder that despite the partial neonic ban there are perfectly legal flowering crops, treated with neonics last year, and are still harming our bees. New research has revealed that our soils are heavily contaminated with these persistent pesticides and they are polluting rivers as well. It is essential for the safety of our bees, pollinators and other wildlife that all neonic seed treatment use is suspended" said Matt Shardlow CEO of Buglife.