How Invasive Species Are Costing the UK Billions

Invasive species are costing the country around £4 billion a year, and more types are becoming established annually. The range of invasive non-native species (INNS) includes Japanese knotweed, signal crayfish and the fungus causing ash dieback.

The UK is now home to about 2,000 INNS and with more species being discovered each year, the problem is growing. Some of Britain’s most familiar but harmful natural intruders aren’t just a nuisance, they’re costing vast sums of money, damaging native ecosystems, and proving very hard to shake off.

Recent research by the Centre of Agriculture and Bioscience International (CABI) has not only revealed the huge annual cost of attempting to deal with them, but the economic, environmental and social impacts that ripple through agriculture, forestry, property, infrastructure, and more. The scale of the issue is rising and so is the urgency to deal with it.

This article explores which invasive species are driving the cost, how they are monitored (or not), what’s being done about them, and where progress is actually being made.

Invasive non-native species

The CABI-led study showed that invasive non-native species such as giant hogweed, signal crayfish and the aquatic water weed floating pennywort, cost the UK around £4bn a year.

The report stated that 10-12 new invasive species establish themselves in the country each year. The species list includes grey squirrel, giant hogweed, mink, parakeets and recent arrivals, marine invasive species such as the sea squirt Didemnum vexillum, along with ash dieback, caused by the fungus Hymenoscyphus fraxineus – which has proved the costliest species to deal with in the past decade in the UK (an estimated £883.5m). This is followed by Japanese knotweed (£246.5m); rabbits (£169.7m); rats and mice (£84.4m); cockroaches (£69.8m) and deer (£62.9m).

The GB Invasive Non-native Species Strategy was drawn up in February 2023 to create a coordinated approach to control invasive species.

The scale of the problem and the real cost of invasive species

The estimate by CABI scientists that in 2021 the cost of INNS to the UK economy was about £4 billion annually, was a jump of 135% since the last comparable report in 2010.

Broken down by sector, the CABI study revealed:

• Agriculture: approximately £1.088 billion
• Commercial forestry: approximately £123 million
• Construction and infrastructure: approximately £270 million
• Tourism and recreation: approximately £136 million

Meanwhile, costs are rising across all nations: England (approximately £3.02 bn), Scotland (approximately £499 m), Wales (approximately £343 m), Northern Ireland (approximately £150 m).

A longer-term study by Queen’s University Belfast puts the bill even higher: over £5 billion over the past 40–50 years, attributing much of that to such species as the European rabbit, Japanese knotweed, and invasive plant species.

These are not fringe species. According to CABI, there are around 2,000 non-native species established in Great Britain, and 10-12 new ones become established each year.

Which invasive alien species are causing the most damage?

Some invasive pest species are well-known, while others fly under the radar. Here are a few of the most economically and ecologically damaging non native invasive species in the UK:

• Ash dieback fungus (Hymenoscyphus fraxineus): this fungus causes ash trees to die and is now the costliest invasive according to the CABI study, estimated at £883.5 million annually. The costs of clearing it from publicly accessible sites, near roads and railways are huge, according to the CABI report.
• Japanese knotweed (Fallopia japonica): first appearing in the UK in the mid-19^th century and used as an ornamental plant, it is found on road verges, riverbanks and derelict land. Japanese knotweed can harm riverbanks and affect the value of properties as it can damage structures with shallow foundations: it’s estimated to cost the UK £246.5 million each year.
• European rabbit: introduced by the Romans about 2,000 years ago, rabbits are a familiar sight in the countryside and cause serious damage by eating grass, crops and burrowing. Their annual cost is estimated in the hundreds of millions.
• Signal crayfish: introduced to UK waterways, these crayfish burrow into riverbanks, destabilise soil, and carry crayfish plague, threatening native, white clawed crayfish. It is vital to halt its spread to protect riverbanks and native crayfish according to Integrated Catchment Solutions Programme, iCASP which pointed out that prevention of an invasive species is always cheaper than the costs of controlling it.
• Floating pennywort: this fast-growing aquatic plant forms thick mats on rivers, increasing flood risk, blocking navigation and damaging biodiversity.
• New invasive flatworms: experts have also warned about land flatworms such as the New Zealand flatworm, which prey on earthworms and soil invertebrates, harming soil health.
• Grey squirrels: this invasive species spread rapidly, competing with red squirrels in their native habitat and forcing them out.
• Muntjac deer: the Reeves’ muntjac deer was introduced to the UK from China in the early 20th century. They negatively impact the environment by eating native plants, competing with native species.

These represent just a fraction of the problem, but they illustrate how problematic species pose a significant threat to many parts of our natural and built environment.

How do we spot and manage the threat of non indigenous species?

Strategy and policy

There is a national framework in place:  The Great Britain Invasive Non-Native Species Strategy 2023 to 2030 which defines invasive alien species, sets out the scale of the risk (economic, environmental, human health), and lays down a vision: to protect ecosystems, people, and the economy by coordinating government bodies, NGOs, researchers, business and the public.

Key goals include early detection, prevention, and control. The strategy covers pest species that are already established and those likely to arrive in future and explicitly links to biosecurity efforts.

Legal and regulatory safety net

• Biosecurity & Border Control: preventing new species invasions is critical. Yet, according to recent figures, less than 1% of the UK’s biosecurity budget is spent on invasive species management measures.
• Great Britain INNS Strategy Compliance: the Strategy calls for rapid-response frameworks, surveillance, risk assessment and pathway management.
• Species‐Specific Controls: certain species are regulated or prohibited; for example, flatworms are emerging targets of biosecurity efforts tied to trade in potted plants.

Monitoring and citizen science

• Non-native species reporting platforms (such as those run by the Non-Native Species Secretariat) help track spread and public sightings.
• Academic research like the CABI study uses economic modelling to estimate cost and scale.
• Local authorities, conservation NGOs, other competent authorities and river trusts also undertake on-the-ground eradication or control projects, often relying heavily on volunteers.

Success stories: when invasive control works

While the problem is vast, there are welcome wins.

1. Signal Crayfish Control in Yorkshire: In some river catchments, trapping and monitoring has slowed the spread. Authorities and trusts work to protect surviving native crayfish, though the fight is ongoing.
2. Floating Pennywort Clearance: local wildlife trusts and freshwater groups in some rivers have cleared pennywort mats mechanically, restoring navigation and improving river flow. Repeated removal helps reduce regrowth.
3. Public Awareness and Reporting: increased public reporting (via apps, local groups) has led to earlier detection of new invasions in many locations, for example, the spotting of mink or giant hogweed in sensitive areas.
4. Policy Momentum: the GB INNS Strategy (2023–2030) itself is a major step forward. By aligning government, science and public actors, it creates a structured pathway for early intervention, funding and coordination.

Why the problem is not easy to solve: the challenges

Even with successes, several major challenges limit progress:

1. Funding Gap
   Despite the huge economic cost, investment in prevention and control is still patchy. The recent biosecurity budget figures show how under-resourced the issue remains.
2. Detection Lag
   Many invasive species are well-established before they’re identified. Detection is difficult, especially in remote or private land.
3. Complex Regulation and Coordination
   The INNS Strategy is a strong framework, but real progress depends on consistent action from multiple agencies, NGOs, landowners, and local councils: coordination is complex.
4. Ecological Trade-offs
   Sometimes, removal of one species can unintentionally disrupt ecosystems. For example, crayfish traps may inadvertently catch native species; chemical control (e.g., herbicide use) can have knock-on effects.
5. Public Engagement and Human Activity
   Many people don’t understand how damaging some “garden weeds” or non-native animals can be. Without broad public involvement, many efforts lack scale.

What needs to change:  expert views on the way forward

• Experts argue that if the UK is serious about tackling invasive species, it needs to invest in prevention and early response, not just reactive control.
• As CABI researchers write: “prevention and early detection, followed by eradication of the highest-risk species prior to establishment” must be the priority.
• The GB INNS Strategy calls for stronger biosecurity, especially at borders and in trade pathways (e.g., horticulture, aquatics).
• Conservationists urge long-term funding for local groups: many invasive control successes happen at the community level but need reliable financial support.

In a report: Stemming the Flood of Invasive Non-Native Species of May 2024, Wildlife & Countryside Link, England’s largest nature coalition, called for the government to triple the budget for invasive species biosecurity to £3m, and provide another £3m to create a dedicated invasive species inspectorate. The report warned that limited resources make control re-active rather than proactive, reducing long term success.

Looking ahead: the significant threat of biological invasions

Progress depends on:

• Growing political will: the publication of the GB INNS Strategy shows the government recognises the major threat of economic or environmental harm posed by alien species.
• More research and innovation: scientists are developing new tools: e-DNA for early detection, bio-control agents, and smarter modelling of high-risk pathways for plants and animals and aquatic organisms.
• Citizen involvement: reporting platforms and public education are helping map invasives more precisely.
• Integrated management: combining biosecurity, habitat restoration, and control gives the best chance. For example, removing pennywort while restoring native riverbank vegetation helps prevent reinvasion.

If effectively implemented, the INNS Strategy could significantly reduce the cost and damage of invasives in coming decades. But experts warn that to avoid losing ground, both scale and equity of response must increase.

How people can be pro-active and help

• Report sightings: if you spot giant hogweed, mink, flatworms or other INNS, report them via official recording apps or local wildlife trusts to help build data to drive action.
• Practice biosecurity: clean boots, tools and equipment when moving between sites (especially water bodies).
• Support local efforts: join or donate to local river trusts, conservation groups or community biosecurity projects.
• Raise awareness: Talk to neighbours, garden groups or local councils about the risks of invasive species.

Prevention methods must scale up

Invasive non-native species might seem to be just weeds in a river or pests in the garden. But behind that is a multi-billion-pound problem, a threat to native biodiversity and a ticking economic burden. Our changing climate is adding to concerns as our environment becomes more attractive to a range of invasive alien species. The good news is that we have the tools, the science, and a national strategy: what we need is the political will – and public engagement – to scale those efforts before the invasion gets any more expensive.

If the right actions are taken, we can hope to turn the tide. If not, our rivers, woodlands and wetlands will continue to pay a very steep price.