Gardeners are set to come under more pressure to ditch a group of pesticides known as neonicotinoids, due to worries over bee colony death.

An investigation at Reading University, backed by Friends of the Earth, found it would cost £1.8billion a year to hand-pollinate UK crops if bees died out altogether.

Bees colonies have declined (credit: WikiMedia)

In April, Amateur Gardening reported how French scientists had claimed that neonicotinoids  (ingredients found in some garden bug sprays) confuse honey bees, interfering with their ability to navigate back to hives.

Bee colonies across Europe have been devastated in recent years, with keepers reporting losses of up to 50 per cent.

Friends of the Earth nature campaigner Paul de Zylva said: “Unless we can halt the decline in British bees, our farmers will have to rely on hand-pollination, which will send food prices rocketing.”

Former Gardeners’ World presenter Toby Buckland opposes the use of neonicotinoids – but has defended gardeners.

Writing in his AG column, Toby said: “I’ve read about the scandalous over-use of neonicotinoids – insect killing chemicals that are now proven to be the reason why bee populations are in decline. I don’t agree with their use, but headlines such as ‘Gardeners perfect roses are killing bees’ impugns the wrong people.

“It’s not gardeners spraying bugs on the odd plant that has caused this catastrophe but some irresponsible farmers who slosh these chemicals around like there’s no tomorrow.”

The Soil Association said it believes there is “already enough evidence to justify an immediate ban on neonicotinoids today”.

Chemical firm Scotts Miracle-Gro, however, has insisted that “multiple factors” affect bee health, including parasitic diseases such as varroa mites, fungal and viral diseases, habitat loss, climatic change and bee-keeping and husbandry practices.

A Scotts statement said: “Their use [neonicotinoids] was suspended in France and then lifted after 10 years as there was no evidence of improvement in bee health when they were suspended.

“These products are widely used in Australia where there are no bee health issues. Strikingly, the Varroa mite is not yet present in Australia.”