Spotting a rat once in your garden is not an infestation. Hearing scratching above the bedroom ceiling at 3am for two weeks running is. This guide walks through the signs that distinguish casual sightings from an established population, the specific health and damage risks that make rats different from mice, and the honest decision tree for when DIY measures are appropriate versus when you need to call a CRRU-compliant professional.
The threshold question
Not every rat sighting is an infestation. UK rats are widespread and individual rats cross gardens, allotments and rural plots routinely. The question that matters is whether you have resident, breeding rats or transient ones.
Signs of resident, breeding rats:
- Multiple droppings in clustered locations (10-20mm capsule-shaped) — fresh droppings are dark and slightly soft; old droppings are dry, lighter and crumble
- Greasy runways along skirtings, behind furniture, on top of cupboards where rats follow the same path
- Gnaw damage that's recent and ongoing — paler exposed wood, ragged plastic edges, chewed packaging
- Sound — scuttling and occasional thumping in lofts, walls or cellars over multiple nights
- Smell — a musky urine odour in nest areas
- Sightings — multiple rats seen over days or weeks, particularly juveniles (smaller individuals indicate breeding)
- Burrows in gardens, allotments, under sheds — fresh soil at the entrance, smooth-walled holes 5-10cm diameter
- Dead rats found — there are usually 5-10 alive for every one dead seen
If you have three or more of these, it's an infestation.
Why rats are different from mice — health and damage
People sometimes assume rats and mice are equivalent problems on different scales. They're not. Rats carry materially higher disease risk and cause materially higher property damage.
Disease risk
- Leptospirosis / Weil's disease. The big one. Spread by rat urine in water and damp surfaces. Causes flu-like illness in mild cases; severe cases can cause kidney failure, jaundice and death. Particularly relevant in Cornwall around rivers, ponds, drainage ditches, harbours and waterways where rats and humans both spend time.
- Salmonella. Contamination of food prep surfaces and food packaging — direct and indirect transmission via droppings, urine and contact.
- Hantavirus. Rare in the UK but documented.
- Toxoplasmosis. Less commonly associated with rats than with cats but possible.
- Allergens. Rat dander and urine proteins trigger asthma and allergic reactions in sensitive individuals.
Property damage
- Wiring damage. Rats chew electrical cabling — documented cause of building fires. Cornwall loft electrics with rat damage are a real fire and insurance issue.
- Plumbing damage. Plastic CWS pipes, soft copper joints and waste pipes all gnawable. A rat-chewed loft tank can flood a house.
- Structural damage. Rats can gnaw through soft mortar, lath-and-plaster ceilings and plasterboard.
- Insulation contamination. Heavy rat activity leaves loft insulation soiled with urine and droppings — replacement cost £400-£2,000+.
- Stored item damage. Cardboard boxes, books, fabric, food storage all gnawed.
The CRRU Stewardship Regime — why amateur rat control is constrained in 2026
From 1 January 2026, the strongest professional rodenticides — Second-Generation Anti-coagulant Rodenticides (SGARs) — are restricted to certified users only. Buyers and users must hold a current CRRU-approved training certificate (less than 5 years old) or be a member of a CRRU-approved CPD scheme. Farm Assurance no longer counts. Sellers won't supply non-certified buyers.
For homeowners, this means:
- Over-the-counter products available to the public are First-Generation Anti-coagulant Rodenticides — significantly weaker than SGARs
- Resistance to First-Generation products is common in UK rat populations
- Effective rat infestation control essentially requires SGAR-strength bait, which requires a CRRU-compliant pro
- SGARs may only be used outdoors when connected to buildings — open-area use is restricted
This is why DIY rat baiting often disappoints: the products available to homeowners are designed for occasional control of light populations, not for clearing established infestations.
The DIY-vs-pro decision tree
DIY likely appropriate:
- Single rat sighting in garden with no other evidence
- Obvious one-off — e.g. building work recently completed, exposed plot now sealed
- Outbuilding-only activity with no main-house involvement
- You're caught early — fresh evidence over 1-2 days only
What to do: snap traps (more humane than glue traps, which are illegal for amateur use since 2024), proofing the obvious entry point, securing food sources, vigilant monitoring for 7-14 days.
Professional treatment needed:
- Multiple signs across two or more weeks
- Loft, cellar or wall-cavity activity
- Food business, holiday let, rental property (documentation matters)
- Health-vulnerable household (young children, immunocompromised individuals, asthma sufferers)
- Water-contact environment (river-adjacent, harbour-side, ditch-fed garden)
- Wiring or plumbing damage detected
- DIY measures haven't cleared the activity within 2 weeks
The Glue Traps (Offences) Act 2022 — what changed in 2024
The Glue Traps (Offences) Act 2022 came into force on 31 July 2024. It bans the use of glue traps by members of the public in England. Professional pest controllers may use them only under licence (Class licence CL53 or Individual licence A15), in exceptional circumstances where alternatives have been exhausted, with documentation and inspection at intervals of no more than 6 hours.
If you bought glue traps before 2024, dispose of them — using them is now an offence. Professional Cornwall pest controllers rarely use glue traps in any case because the licence regime is restrictive and alternatives are usually sufficient.
What professional treatment costs
Indicative Cornwall pricing for established rat infestations (2026):
- Standard 2-3 visit domestic programme: £200-£400
- Rural property with multiple outbuildings: £250-£500
- Severe infestation with multiple harbourages: £300-£800+
- Commercial site: quoted on site survey
- Add £80-£200 for dead body removal from sealed voids if needed
- Add £200-£800 builder costs for separate proofing work
Common Cornwall rat infestation patterns
- Coastal harbour villages — Mevagissey, Mousehole, Newlyn, Port Isaac. Older fishing-village construction, food waste from restaurants, harbour-side wharves.
- Rural smallholdings — chicken runs, horse feed stores, multiple outbuildings, compost heaps. Year-round food supply.
- Holiday lets with food waste accumulation between guests and after parties
- Allotment-adjacent properties — Truro, Falmouth, Penzance. Allotment compost heaps and feed waste sustain populations that move into nearby houses.
- Stream and river-side properties — riparian rats with established burrow networks
- Old industrial sites — Camborne, Redruth, Hayle. Legacy granaries and mill buildings.
What good rat control looks like
The full sequence:
- Survey — identify entry points, harbourage, food sources, evidence of population scale
- Treatment — bait stations and/or snap traps at active points; CRRU-compliant SGAR use where appropriate
- Monitoring — 2-3 follow-up visits at 10-14 day intervals
- Proofing — separate worklist of structural fixes (sealing pipes, meshing vents, replacing brush strips, cutting climbing routes)
- Clearance confirmation — no fresh activity for 7-10 days
- Documentation — written report covering CRRU compliance, work done, recommendations
- Aftercare — 30-90 day callback guarantee
Get matched with a Cornwall rat specialist
If you've got two or more of the signs above, the right step is a Cornwall pest control survey. Submit your postcode on the quote form; we match you to a CRRU-compliant Cornwall pest controller in your area. See related: prevention guide, rats in the attic, rats in the garden, rat control service.