What do I do if I lose the only key to my car?

What it actually costs and takes to replace a lost key, why a dealer is not always the answer, what proof of ownership you will need, and how to make the second key stop being optional.

Difficulty: beginner
Time: 25 min
Read: 5 min
Safety: caution

Short answer

You have two routes: the main dealer, who will order a key coded to your car, or a mobile auto locksmith, who can usually come to the vehicle and often costs less. Both will require proof that the car is yours — usually the V5C in your name plus photo ID — and both will normally delete the lost key from the car's memory so it cannot be used. Get a second key cut and programmed at the same time; doing two at once is far cheaper than doing one twice.

Losing the only key to a modern car is expensive in a way that surprises people, and the reason is worth understanding. There is no longer a key that a locksmith can copy from a blank. There is a mechanical blade, which is often laser-cut to a code held by the manufacturer, and there is a transponder chip that has to be introduced to the car's immobiliser through a security procedure that requires access to manufacturer data. On some cars the whole key set has to be relearned, which invalidates any keys still in existence — a good thing when one has been stolen and an annoyance when you find the original a week later.

Safety

If a key is lost rather than mislaid, treat the car as potentially compromised — particularly if anything with your address on it was lost at the same time, or if the key was taken. Move the car if you can, or at minimum use a physical steering lock, and tell your insurer. Never leave a spare key hidden on or near the vehicle: it is the first place a thief looks and it can invalidate a claim.

Step by step

Search properly before spending money.The overwhelming majority of "lost" keys turn up. Coat pockets, the bin, the washing machine, under a car seat, at the last shop you visited. Ring the venues you visited and the local council or police lost property, and check whether the fob has a Bluetooth tracker on the keyring.
Secure the car in the meantime.If the key may have been stolen along with anything showing your address, treat the car as at risk. Park it somewhere secure or blocked in, fit a steering lock, and consider whether the insurer needs to know now rather than later.
Find your paperwork.Whoever replaces the key will need to establish you are entitled to it. That normally means the V5C registration document in your name and photo identification matching it. If the V5C is not in your name yet, or is missing, sort that first — nobody reputable will cut a key without it.
Get quotes from both a dealer and an auto locksmith.A franchised dealer orders a key against the vehicle identification number and codes it, usually with the car recovered to them. A mobile auto locksmith comes to the car and often has the equipment for the same job. Prices differ substantially between them and between makes, so it is worth two calls.
Ask specifically whether the old key will be deleted.If the key was stolen or lost in a public place, you want the lost key erased from the car's immobiliser so it cannot start the vehicle. Not every job does this by default — ask for it explicitly, and expect it to require all remaining keys to be present.
Have a second key made at the same time.Most of the cost is the visit and the programming session, not the key. Doing two at once is dramatically cheaper than coming back later, and it removes the whole problem permanently. This is the single most useful thing in this guide.
Check whether your insurance or breakdown cover helps.Some comprehensive policies include key cover, sometimes as an add-on, and some breakdown policies include a contribution towards lost keys or a locksmith call-out. Many people pay for cover they already have. Check the schedule before you book anything.
Store the spare somewhere sensible.Not on the same keyring, not in the car, and not hidden in the wheel arch. A drawer at home, and a photograph of the key code if the manufacturer supplies one. If the car is keyless, keep the spare in a signal-blocking pouch or tin like the everyday one.

Common mistakes

Only ever having one key — It converts a lost key from an inconvenience into a recovery, a dealer visit and a large bill. A second key is cheap when ordered alongside the first and expensive as an emergency.
Hiding a spare key on or near the car — Wheel arches, bumpers and under plant pots are the first places checked, and an insurer that establishes the car was taken with a key left accessible is very likely to decline the claim.

If it doesn't work

The car has been locked with the keys inside

Cause: A different problem from a lost key — Fix: Do not break a window unless there is a child or an animal inside, in which case call 999. Otherwise a breakdown provider or an auto locksmith can usually open a car non-destructively, and many policies include it.

Locksmith says the immobiliser needs all keys present

Cause: Some cars relearn the whole key set rather than adding one — Fix: Bring every key you still have to the appointment. Any key not present becomes useless, which is exactly what you want for a stolen one and a nuisance for a mislaid one.

V5C is not in your name

Cause: Recently bought and the transfer has not completed — Fix: You will struggle to get a key cut. The new keeper slip and the sale receipt may be accepted by some, but expect to have to complete the change of keeper first.

Cheap fob bought online will not program

Cause: Wrong frequency, wrong chip type, or a locked used fob from another car — Fix: Buy the key through whoever is programming it, or check with them before ordering. Used fobs from other vehicles are frequently locked to the original car and cannot be reused.

Keyless car, key lost, car is not at home

Cause: It cannot be driven and may not be able to be opened without damage — Fix: A mobile auto locksmith is the usual answer, and recovery to a dealer is the fallback. This is where breakdown cover with a key provision genuinely earns its money.

Questions people ask

How much does a replacement car key cost?

It varies widely by make and by whether it is a basic transponder key or a keyless smart fob, and between a dealer and an auto locksmith. It is enough money that getting two quotes is worthwhile, and enough that having a spare made proactively is one of the better value decisions in car ownership.

Can any locksmith cut a car key?

No. It needs an auto locksmith with vehicle-specific equipment and access to the manufacturer's security data. A high-street key cutter can copy a mechanical blade, but that blade will open the door and not start the engine.

Does losing a key affect my insurance?

Losing one is not normally something you must declare in itself, but a theft claim on a car taken with its own key is treated very differently from one taken by force. If a key has been stolen, tell your insurer, and have the lost key deleted from the car.