Wildlife conservationists are calling for a ban on importing foreign soil to the UK to stop non-native invasive species contributing to the decline of British nature.

Insects, seeds and microorganisms can hitch a ride on soil, compost and potted plants and threaten to outcompete with or prey upon native species, the Wildlife Countryside Link (WCL) said.

More than 350,000 tonnes of plants and soils were imported to the UK in 2021 and of this, 287,000 tonnes came from the EU, which does not allow imports of UK soil to protect its wildlife.

WCL said the UK should take a similar approach given that it was ranked in the bottom 10% of countries worldwide for its biodiversity health by the Natural History Museum and because non-native species are a key driver of biodiversity loss.

Prevention is much easier and cheaper than attempting to find a cure when it comes to dealing with these invasive threats

Richard Benwell, chief executive of WCL, said: “Invasive species are a growing threat to wildlife in the UK. It only takes one or two eggs or a few spores hidden in imported soils to introduce organisms that can play havoc on our ecosystems.

“Once they have a foothold, it’s hard to stop damage spreading, but prevention is possible and so much more affordable.

“Phasing out imports of soils would help prevent further disasters like ash dieback. As part of a robust strategy to hold back and root out invasive species, this is an essential part of any plan to halt the decline of nature.”

Experts have identified the New Zealand flatworm, which eats native earthworms; the Spanish Slug, a “voracious eater of crops, wild and garden plants”; and the harlequin ladybird, which has displaced native ladybirds leading to a reduction of two-thirds over 10 years.

The ash dieback fungus has also been affecting native ash trees since it was first recorded in the UK in 2012.

It is estimated that up to 95% of ash trees will be wiped out while Oxford University researchers predicted this will cost the country £15 billion in clear-up costs as well as lost benefits such as water and air purification and carbon sequestration.

Joan Edwards, director of policy & public affairs at The Wildlife Trusts, said: “Both the UK economy and the natural world are paying a steep price for the impact of invasive species.

“Nature soil invaders are already hitting British wildlife hard, out-competing and eating species from our beautiful but rare lilies and fritillaries, through to gardeners’ friends like ladybirds and earthworms.

“The economic cost of invasive species is more than £2 billion a year, impacting shipping, rivers, recreation, timber and even the gin industry.

“Closing a major route to entry to the UK, by banning soil imports, makes good economic sense and is vital for nature’s recovery.”

Other species that have been identified as an emerging risk to native UK plants includes the Japanese beetle, the larvae of which live in soil and can be easily moved with rooted plants.

WCL said these beetles have caused major damage to apple, birch, lime and rose in North America with maples, birch, apples and other stone fruit trees at risk in the UK.

Current summer temperatures are thought to be too cool for the beetle to thrive in the UK but this may change as increasingly hotter summers become more common through climate change.

Alisha Anstee, lead policy advocate of tree health and invasive species at Woodland Trust, said: “The introduction of invasive species including certain tree diseases is one of the most serious threats to trees and other wildlife in the UK.

“The UK is suffering the impacts of many imported invasive species, some of which can travel undetected in the soil.

“It is likely that Phytophthora ramorum, which is causing larch dieback, arrived via the plant trade and this disease is now leading to mass tree loss.

“Prevention is much easier and cheaper than attempting to find a cure when it comes to dealing with these invasive threats.”