A laid-up car is warm, quiet, undisturbed and full of soft material, which makes it close to ideal for a mouse. Most of the popular remedies have little or nothing behind them. This is what actually works, what the evidence says about the folklore, and where you stand with an insurer if they have already been in.
Damp gets all the attention in storage advice, and on a T-Type with an ash frame that is fair enough. Rodents get a single line about bunging the exhaust, and then everyone moves on.
The claims data suggests that is the wrong way round. Aviva, reviewing its motor claims for 2023 and 2024, reported a 28 per cent rise in rodent-related damage, an average claim of £2,494 in 2024 against £2,253 the year before, and one case exceeding £24,000 in which the car was written off. Those are ordinary cars. A period loom, an ash frame and a leather interior do not make the bill smaller.
The detail in that data which matters most to anybody reading this is when it happens. The claims spike in December and January, which is precisely the period a classic spends laid up and unvisited.
Why a stored classic is such a good target
A mouse wants warmth, quiet, safety and something to build a nest from. A car under a cover in a closed garage between October and April supplies all four, and a T-Type supplies the fourth more generously than most.
The wiring of the period is cotton braided over rubber. The seats and trim are leather over horsehair and felt. The hood, tonneau and sidescreen surrounds are fabric. The frame itself is ash. Almost every material a rodent wants for nesting is present, and the car is left undisturbed for months at exactly the time of year they are looking for somewhere to spend the winter.
The damage that follows is rarely a single chewed cable. It is a nest in the air filter or on the manifold, insulation stripped from a loom that is no longer available off the shelf, droppings and urine soaked into padding that has to come out to be cleaned, and a smell that attracts the next one.
What actually works
None of this is exotic. It is exclusion, removing what attracts them, and looking regularly.
Seal the building, not the car. Oxford City Council, in its public pest control guidance, puts the figure at gaps as small as 6 mm, the sort of opening left around a pipe or under a door. That is the number to hold in your head when you walk round the garage. A door with daylight under it is an open door.
Take away the nesting material. Cardboard boxes, old carpet, bags of rags, loft insulation, seed and pet food stored in the same building. A garage that is tidy and swept is a much less attractive proposition than one with soft material stacked in the corners, and this costs nothing.
Take away the food in the car. Anything organic in the cabin, including a forgotten sweet in a door pocket, is a reason to move in.
Block the obvious ways in. The exhaust tailpipe and the air intake, with something brightly coloured hanging from it so that it cannot possibly be forgotten in the spring. This is already in Storing Your MG T-Series, and it remains sound.
Set traps and check them. Traps only work if somebody looks at them. Poison bait carries risks worth thinking about in a domestic garage, both to pets and through secondary poisoning of owls and other wildlife that eat a poisoned rodent, so it is not the obvious first choice it appears to be.
Visit the car. Disturbance is itself a deterrent, and a monthly look is the difference between a nest you remove and a loom you rewire. It is also when you would notice a dehumidifier that has stopped or a cover that has slipped.
The remedies that get recommended, and what is behind them
This is a field thick with confident advice. Very little of it survives being looked into.
Ultrasonic repellers. McGill University's Office for Science and Society is blunt: the devices have never been proven to work. Laboratory work at high intensities is not reproduced by consumer units, studies of the commercial products are limited and frequently have no control, and animals habituate to the sound or ignore it from the outset. The United States Federal Trade Commission has previously warned manufacturers and retailers over the claims made for them. If one is running in your garage, it is doing nothing you can rely on.
Mothballs. In the United Kingdom this is not a question of whether they work. Naphthalene mothballs are not legal to sell here. The Office for Product Safety and Standards published a product safety report in August 2024 on an imported brand, recording that the product contained naphthalene, a banned carcinogenic substance, that it failed to meet the requirements of REACH, and that the stock was seized and destroyed. Anything sold as a mothball in a British shop today is a different chemistry, and none of it is a rodent repellent.
Peppermint oil. The most recommended remedy of all, and the one where no independent evidence could be found either way. What is easy to verify is who is doing the recommending: search for it and the results are dominated by retailers selling peppermint rodent products and by forum threads repeating each other. That is not proof it fails. It is a reason not to rely on it as your only measure, and it is worth noticing that a strong smell in a stored car has costs of its own on leather and fabric.
Dryer sheets, human hair, and the rest. Same position as peppermint oil, with less behind them.
If they have already been in
Do not start the engine until you have looked. A nest on the manifold or in the air intake is a fire risk, and a chewed loom can short the moment the battery goes back on.
Check, in this order: the air filter and intake, the exhaust tailpipe, around and on top of the engine, the loom wherever it runs near warmth, under the seats and in the seat padding, the hood and tonneau where they are folded, and the boot or luggage area.
On cleaning up, treat droppings and urine as a health matter rather than a mess. The standard public health advice is not to sweep or vacuum them dry, because that puts particles into the air. Dampen first, wear gloves, ventilate the space, and wash afterwards.
Then deal with the smell properly, because residual scent marks the car as somewhere a rodent has already been and lived.
Where you stand with an insurer
This is where the numbers get uncomfortable, and it is the part most storage advice omits entirely.
Which? reports that most comprehensive policies will pay out for rodent damage, while stressing that cover varies and that the policy wording is what decides it. Aviva says the same in its own words, that cover varies from insurer to insurer and the policy should be checked. Neither is a guarantee about your policy.
Three things are worth establishing before you need to know.
Whether your policy covers it at all. Damage by vermin is a standard exclusion in some policies and not in others. It is a question with a definite answer, and the time to get it is not while looking at a chewed loom.
What happens in the winter. Many classic owners reduce cover while the car is laid up. If yours does, ask specifically what that reduced cover includes, because the claims peak in December and January is the same period the car is sitting on it. That is the single most useful question in this article and almost nobody asks it.
Whether you would actually claim. With an average claim around £2,500, a typical excess and the effect on a no-claims discount, Which? makes the point that claiming is not automatically the right move. On an agreed-value classic policy the sums may work differently again.
None of this is insurance advice, and this archive is not qualified to give any. It is a list of questions to put to your own insurer or broker, whose answer about your own policy is the only one that counts. The archive general notes on insuring a T-Type are on the insurance page.
What is not established
- Whether peppermint oil deters rodents. No independent controlled evidence was located in either direction.
- Whether period cotton-braided looms are more or less attractive to rodents than modern insulation. Much has been written about soy-based insulation in modern cars, and none of it transfers to a car of this age. No study of period looms was found.
- Whether any particular classic policy covers vermin damage. This varies by insurer and by policy and cannot be generalised.
- The rodent claims figures are for the whole motor market, not for classics specifically. No classic-specific claims data was located.
If you have had rodents in a T-Type, what they went for and what the repair cost, that experience would be worth publishing here, credited to you by name.
Sources
- Aviva, "Rodent-related motor claims increase by over a quarter", news release, October 2025, quoting James Driscoll, Motor Claims Manager
- Which?, "Rodent damage claims rise: will your insurance cover you this winter?"
- Office for Science and Society, McGill University, "Are ultrasonic pest repellers effective?"
- Office for Product Safety and Standards, Product Safety Report 2408-0123, mothballs containing naphthalene, August 2024
- Oxford City Council, pest control advice, mice