Mice in your London flat this autumn: why October, how they get in and what works

Mice turn up in London flats in October because the nights get colder and a heated building with food in it beats a garden or a railway bank. A house mouse can get through a gap of 5mm, so once one finds a pipe run or a crack behind a kitchen unit, the rest of the building is open to it. If you are seeing droppings now you are not unlucky: mice in a flat are the classic October to February problem, and the sooner the building is surveyed and sealed, the shorter the job.

Why do mice come into flats in October?

Because the temperature drops and the food outside runs out. One national pest control firm reported rodent call-outs up 50% in August to October 2022 against the year before, continuing into Christmas, and put it down to falling temperatures pushing rodents indoors. The National Pest Technicians Association's autumn 2025 survey found mouse activity up 29% on average, with the rise strongest in London, the South East and the North West.

Westminster City Council's mouse leaflet says nests are "often built inside houses, especially during the winter", under floors and in lofts, made from cloth, wool and paper. In a city where so much of the housing is flats, somebody else's kitchen is often the nest site and yours is the feeding ground.

How do mice get into a flat?

Through gaps you would not think to look at. The Westminster leaflet gives the figure to remember: mice can squeeze through cracks as small as 5mm, and a mouse hole is normally only 20 to 30mm across. Mice climb well, so a gap at ceiling height is as useful to them as one at the skirting board.

In a London flat the usual routes are:

• Pipe runs where water, gas and waste pipes pass through walls and floors, especially behind the kitchen units and under the bath.
• Boxed-in services in purpose-built blocks, which run floor to floor and are rarely sealed at every level.
• Victorian terraces split into flats, like the Abbeville grids of Clapham, where floor voids, chimney breasts and party walls connect the whole house.
• Gaps under front doors, around meter cupboards and at ground-floor bin stores.
• Converted houses in Kensington, where large Georgian and Victorian houses were divided into flats and the services were added later, and the mansion blocks of Pimlico, where Dolphin Square alone holds 1,250 flats.

What are the signs of mice in a flat?

Droppings are the first sign most people notice, and they tell you which rodent you have. Mouse droppings are black, rod-shaped and 3 to 6mm long, scattered rather than piled; rat droppings are much larger, up to 12mm and tapered at both ends. Other signs:

• Dark smear marks along skirting boards and pipe runs, left by fur rubbing the same route night after night.
• Gnawed packaging in cupboards, particularly cereals, which are a mouse's preferred food.
• Scratching or scuttling behind the kitchen units or in the ceiling void after dark.
• A stale smell in cupboards, which is urine: male mice mark their territory with it.
• Shredded paper, cloth or insulation where a nest is being built.

Is one mouse ever just one mouse?

Almost never, because of how fast house mice breed indoors. The Mammal Society says that in buildings litters are born at roughly monthly intervals, all year round, while mice living outside breed only in summer. Each litter is five to eight young, weaned by 23 days, and Westminster's leaflet puts it at five to ten litters a year per female.

So a pair that moved in during the first cold week of October can be twenty mice by Christmas, with the first daughters close to breeding themselves. This is why the mouse you saw once in the kitchen tends to become droppings in the bedroom within a month, and why waiting to see if it comes back costs weeks.

Are mice in a flat a health risk?

A modest one, but a real one, mainly through what they leave on surfaces. The NHS lists mice among the animals whose urine spreads leptospirosis, which enters through the mouth, eyes or a cut. It is rare: the UK Health Security Agency counted 115 cases in England in 2025, and most people infected have no symptoms or a mild flu-like illness.

The precautions are the ones the NHS gives: cover cuts with waterproof plasters, wash hands after cleaning up, and never handle a dead rodent bare-handed. Clean droppings with gloves and a disinfectant rather than a dry brush, and keep food in sealed containers until the programme is finished.

Why do DIY poison and glue traps fail?

Because the first is often ineffective against London mice and the second is now a criminal offence. Setting a glue trap to catch a rodent in England has been an offence since 31 July 2024 under the Glue Traps (Offences) Act 2022. Licences exist only for professional pest controllers in settings such as hospitals and critical infrastructure, and the BPCA's guidance states plainly that dwellings are not covered. Hounslow Council now asks residents to remove any glue boards before its officer arrives, because it cannot lawfully use them in homes, and nor do we.

Shop-bought poison has two problems. Resistance to the actives in amateur baits, bromadiolone and difenacoum, is documented across central southern England, and since 1 January 2026 the stronger professional products can only be bought on proof of competence, so what is on the shelf is weaker and in smaller packs than it was. Mice are curious and readily interact with traps, which is why a professional programme for mice leans on trapping and proofing rather than bait alone.

What does a professional mouse programme in a flat involve?

A survey first, then treatment and proofing together, then a follow-up to confirm it has stopped. The pattern councils and the trade work to is two to three visits over a few weeks, with follow-ups seven to ten days apart; Westminster's leaflet says most mouse infestations take four to eight weeks to control. Ours runs like this:

1. Survey the flat and the routes into it: behind the kitchen units, the pipe runs, the meter cupboard, and the communal areas if we can get access.
2. Set traps and, where appropriate, tamper-resistant bait stations placed where children and pets cannot reach them, applied to label with the room clear for the stated time.
3. Seal the entry points found on the survey with materials a mouse cannot chew through, including the gap behind the washing machine that everybody forgets.
4. Return to check activity, clear the traps and finish any proofing that needed the first visit's evidence.

Every treatment carries a written six-month guarantee, subject to the site survey. Rodenticides are used to the CRRU UK code, which since January 2026 requires a current certificate to buy them at all.

What should you do if you rent or live in a block?

Tell the managing agent or landlord in writing the day you see the signs, because in a block the problem is almost never confined to one flat. Shelter's advice is that your landlord must deal with an infestation caused by a repair they must fix, and must keep the home fit to live in throughout the tenancy; if the mice were there when you moved in, that is theirs too. A landlord does not usually have to deal with pests coming from a neighbouring property, which is exactly why the freeholder or managing agent needs to treat the building, not the flat.

If you are a council tenant in Kensington and Chelsea the council treats rats and mice inside the building without charge, and Camden gives its tenants up to two visits free. Private tenants and leaseholders mostly pay, and in Westminster the council is not taking on private work at all. The owner's side of all this is in our guide for London landlords.

What to do next

Book a free inspection survey and we will tell you where they are getting in before anything is quoted. We work Monday to Saturday, 8am to 7pm, often same day, on 020 3411 2329. See the mouse control page for how a programme runs, and the rat control page if the droppings are the bigger, tapered kind.