The quick answer

The four active ingredients you'll meet most often in UK DIY pest control are Brodifacoum, Difenacoum and Bromadiolone, which are anticoagulant rodenticides used against rats and mice, and Permethrin, an insecticide used against fleas, bed bugs, moths, cockroaches and flies. The three rodenticides all work by stopping blood from clotting. Permethrin works on the insect nervous system. All four are regulated products, so the important thing is matching the active to the pest and following the product label.

What an active ingredient is

The active ingredient is the part of a product that actually does the work. Two bait boxes can look identical but contain different actives, and that changes how potent they are, which pests they suit and how they need to be handled. Knowing the active also helps you avoid doubling up on the same chemistry or using something on the wrong pest.

Brodifacoum

Brodifacoum is a second generation anticoagulant rodenticide. It's one of the more potent rodent baits available for amateur use, which is why it's effective where mice have been ignoring weaker baits. Like all anticoagulants it works by blocking the vitamin K cycle, which stops the blood clotting. It's a slow acting bait by design, so rodents keep feeding rather than learning to avoid it.

Brodifacoum is the active used in the Pest Help mouse kits, both the Mouse Killer Poison Kit Small and the Mouse Killer Poison Kit Large. Because it's potent and persistent, it should always be used in locked bait stations, kept away from children, pets and non target wildlife, and used strictly to the label.

Difenacoum

Difenacoum is also a second generation anticoagulant, working the same way by disrupting blood clotting, but it's generally less potent than Brodifacoum. That makes it a common choice for rats and mice in and around homes where a slightly milder bait is appropriate. It's one of the most widely available anticoagulants in UK amateur products.

In practice you'll often see Difenacoum and Brodifacoum talked about together, because they're both second generation anticoagulants used for the same pests. The main difference is potency and persistence, not the basic way they work.

Bromadiolone

Bromadiolone is another second generation anticoagulant, broadly similar to Difenacoum in strength, and used against rats and mice. It works in the same anticoagulant way, blocking the clotting cycle so the rodent succumbs after feeding. It's commonly found in rat baits used in and around buildings, though the exact active varies by product.

For rat activity around the home, garden or outbuildings, the Pest Help Rat Killer Poison Kit Small and Rat Killer Poison Kit Large provide secure bait stations sized for rats. Check the active named on each product label, and never mix rodenticides without reading both labels.

The three rodenticides compared

All three are second generation anticoagulants and all three kill in the same way, by stopping the blood clotting after the rodent feeds. The practical differences are potency and persistence. Brodifacoum is the most potent, which is useful for stubborn mouse activity. Difenacoum and Bromadiolone are slightly milder and very common in everyday rat and mouse baits. For a typical UK home you don't need to agonise over which anticoagulant to pick. It's more important to use enough bait stations, place them on the active routes, and keep feeding going until activity stops.

Permethrin

Permethrin is a synthetic pyrethroid insecticide, and it's the odd one out here because it targets insects, not rodents. It works on the insect nervous system, affecting the sodium channels in nerve cells, which is why it acts quickly against a broad range of insects. It's used against fleas, bed bugs, moths, cockroaches, cluster flies and other crawling and flying insects.

Permethrin is the active behind the Pest Help Total Insect Fumigation Pack, which uses smoke generators to carry the active into the gaps a spray can't reach, under floorboards, behind units, into carpet pile and across a whole room. One important caveat: Permethrin is toxic to cats and to fish, so keep cats out of treated rooms until they're ventilated and aired, and never let it get near aquariums or ponds.

Safety and the law

Rodenticides such as Brodifacoum, Difenacoum and Bromadiolone are regulated biocidal products. In Great Britain the Health and Safety Executive covers them under product type 14 of the GB Biocidal Products Regulation, and there's a stewardship regime around their use. Always follow the product label, use locked bait stations, and dispose of any dead rodents and unused bait responsibly. You can read the HSE rodenticide guidance for the legal position.

Insecticides like Permethrin are regulated too, and the same principle applies: read the label, use only as directed, and pay attention to the warnings, especially around cats, fish and ventilation. Whatever the active, matching it to the right pest and using it to the label is what keeps treatment both effective and safe.

FAQ

What's the difference between Brodifacoum and Difenacoum?

Both are second generation anticoagulant rodenticides that kill rats and mice by stopping the blood clotting. Brodifacoum is more potent and persistent, which suits stubborn mouse activity. Difenacoum is slightly milder and very common in everyday rat and mouse baits.

Is Permethrin safe to use at home?

Permethrin is widely used in home insect products, but it's toxic to cats and to fish. Keep cats out of treated rooms until they've been aired, keep it away from aquariums and ponds, and follow the product label.

Which active ingredient do I need for mice?

Mouse baits commonly use anticoagulants such as Brodifacoum or Difenacoum. The Pest Help mouse kits use Brodifacoum. The active matters less than placing enough bait stations on the routes mice actually use.

Can I mix different rodenticides?

Read both labels first and do not combine products unless the labels allow it. In most home situations you don't need to mix, you just need enough correctly placed bait stations and to keep feeding going until activity stops.

What we'd do next

If you're dealing with mice, the Pest Help mouse kits use Brodifacoum and come in a small 4 box version for early activity and a large 8 box version for larger or spread out problems. For rats, use the rat kits with their larger stations. For insects, the Total Insect Fumigation Pack uses Permethrin smoke generators. Whatever you choose, match the active to the pest and follow the label.