Leaving your car running to defrost: is it illegal, and will insurance pay if it is stolen?

Car News11/13/2026
Is it illegal to leave your car running to defrost? | Rooster

On a frosty morning, starting the car and nipping back inside for a cup of tea while the windscreen clears seems harmless. But it can break the law, and if a thief drives off with your car, your insurer may refuse to pay out.

This guide explains the rules on idling and unattended cars, how insurance treats keys-in-the-car thefts, and the quickest legal ways to defrost.

Last updated 9 November 2026. Rules come from the Highway Code and the Road Vehicles (Construction and Use) Regulations 1986.

Key takeaways

  • On a public road, you must not leave a vehicle unattended with the engine running, or run the engine unnecessarily while stationary (Highway Code Rule 123).
  • The offences come from regulations 98 and 107 of the Road Vehicles (Construction and Use) Regulations 1986.
  • Fixed penalties are usually £20, and can be higher in some areas, including parts of London.
  • On a private driveway the idling rules do not apply, but leaving the car running unattended is still a theft risk.
  • Most policies exclude theft if the keys were left in or on the car, so a stolen car might not be covered at all.

In this guide

What the law says

Highway Code Rule 123 says you must not leave a parked vehicle unattended with the engine running, or leave a vehicle engine running unnecessarily while that vehicle is stationary on a public road.

This is backed by two rules in the Road Vehicles (Construction and Use) Regulations 1986:

  • Regulation 98 covers running the engine unnecessarily while stationary (often called idling).
  • Regulation 107 covers leaving a vehicle unattended without stopping the engine.

Local councils and police can issue fixed penalty notices. The standard penalty is £20, and some councils, particularly in London, can charge more. In practice, many officers will ask you to switch off first, but you can be fined.

Does it apply on my driveway?

The idling and unattended vehicle rules apply on public roads. If your car is on your own private driveway, you are not breaking these rules by letting the engine run.

But the theft risk is the same, or even higher, because thieves know that a car with misted windows and exhaust fumes on a cold morning may have keys in it.

Will insurance pay if my car is stolen while defrosting?

Often, no. Most car insurance policies have an exclusion for theft when:

  • the keys were left in, on or near the car
  • the car was left unlocked or with windows open
  • the engine was running and the car unattended

This type of theft is sometimes called frost-jacking. If your car is taken this way, your insurer may refuse the claim, leaving you with no car and the outstanding finance still to pay. Check the theft section of your policy wording to see exactly what it says.

If your car is stolen, report it to the police straight away and then tell your insurer. Our guide to what happens if your car is stolen explains the next steps.

Quick, legal ways to defrost your car

  1. Stay with the car. It is fine to run the engine while you clear the windows, as long as you are right there and it is not running unnecessarily.
  2. Use the heater and air conditioning together. Air conditioning dries the air and clears mist faster. Point the vents at the windscreen.
  3. Use a scraper and de-icer spray. Start the de-icer working while you clear the roof and lights.
  4. Use heated screens if your car has them.
  5. Cover the windscreen the night before. A windscreen cover, old towel or piece of cardboard held in by the doors stops frost forming.
  6. Do not use boiling water. It can crack the glass and refreeze on the ground.
  7. Use pre-heating if you have an electric or hybrid car that allows it from an app while plugged in. You can stay inside and the car stays locked.

For more ideas, see our guide on how to demist and defrost your car windscreen.

Frequently asked questions

Can I leave the car running if I am sitting in it?

Yes, while you are defrosting the windows. You are not leaving it unattended, and clearing the glass so you can see is a good reason to run the engine. Switch off once you are ready to go or if you are waiting for a long time.

Is remote start legal in the UK?

Remote start and app pre-heating features are not illegal in themselves, but leaving an engine running on a public road unattended is still covered by the rules above. Electric pre-heating while plugged in at home does not involve a running engine.

What should I do if my car is stolen from my drive?

Call the police on 999 if the theft is happening, or 101 afterwards, and get a crime reference number. Then call your insurer and tell your finance company if you have one.

Sources and further reading