The UK is experiencing a record-breaking heatwave, with a red weather warning in place and temperatures reaching 36.7°C in Somerset. Many drivers are tempted to sit in their parked cars with the engine running to keep the air conditioning on, but this could lead to a fine.
Is it illegal to idle your car?
According to the RAC, drivers who sit in stationary vehicles with the air conditioning running risk a fine for breaking vehicle emissions laws. Rule 123 of the Highway Code states: "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."
The RAC warns that remaining in a vehicle with its engine idling causes air pollution and is punishable with a fine of up to £110 for people who refuse to switch off after being asked. Generally, if the vehicle is stationary for more than a couple of minutes, you should apply the parking brake and switch off the engine to reduce emissions and noise pollution.
Exceptions and regional differences
This rule does not apply if you are stationary due to traffic queues. However, the consequences differ depending on where you are in the UK. In Wales, the Welsh Government is increasing the current £20 fixed penalty fine to a higher bracket of £75 to £150 from 30 September 2026. It specifically states that "unacceptable reasons for idling" include operating heating or cooling systems for comfort.
The RAC notes that the standard penalty for engine idling across the UK is a fixed penalty notice ranging from £40 to £80, with fines typically halved if settled promptly. Some councils, such as Islington and Westminster in London, have imposed heftier fines of up to £110.
Expert advice and potential leniency
RAC senior policy officer Rod Dennis commented: "Air conditioning is a game-changer in modern vehicles, making otherwise uncomfortable journeys by road a genuinely pleasant experience. We even advise those driving vehicles without air-con to consider delaying any non-essential trips this week until the heatwave passes. But while we're all desperate to stay cool, just sitting in the car with the engine and air conditioning running and going nowhere isn't advisable. Due to the air pollution this causes, you risk a fine from a police or civil enforcement officer."
Given the extreme conditions, police or enforcement officers may show some leniency, but the risk of a fine remains.
