You could be committing an offence
Large parts of the UK are experiencing an unprecedented heatwave, with the southern regions of England and Wales bearing the brunt of the extreme conditions. A red weather warning has been in effect since Wednesday morning and has been prolonged to Friday across certain areas.
Schools have shut their doors, rail services have been disrupted and the public has been advised against making non-essential journeys. The UK recorded its hottest June day ever when the mercury soared to 36.7°C at Merryfield, Somerset on Thursday.
With such extreme conditions, attempting to remain as comfortable and cool as possible under the circumstances will be amongst most people’s main concerns.
And with time spent in parked cars an unavoidable reality for many – whether waiting to collect a friend or children from school – that might involve leaving the engine on to maintain air conditioning, reports Wales Online.
But does this breach regulations and could motorists face potential consequences?
Am I permitted to leave my engine running while stationary?
The RAC warns that “drivers seeking to cool down by sitting in stationary vehicles with their air-con are running the risk of a fine for breaking vehicle emissions laws”.
It states: “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.”
The penalties vary depending on which part of the UK you’re in
Generally speaking, 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.
“Generally, if the vehicle is stationary and is likely to remain so for more than a couple of minutes, you should apply the parking brake and switch off the engine to reduce emissions and noise pollution.”
This doesn’t apply if you’re stationary due to traffic queues
In Wales, the Welsh Government is increasing the current £20 fixed penalty fine to a higher penalty range of £75-£150 from 30 September 2026. It states: “Many people are not aware that stationary idling is an offence. We are working to address this by raising awareness and encouraging drivers to switch off, when stationary.”
It specifically states that “unacceptable reasons for idling” include “operating heating/cooling systems for comfort”.
It further explains that its rationale for raising the fine includes that idling “creates air and noise pollution which is harmful to public health”, “contributes to a range of problems including heart and lung diseases” and that “children, young people and people with existing health conditions are particularly vulnerable”.
The RAC states that the standard penalty for engine idling across the UK (though not universally applicable) is a fixed penalty notice ranging from £40-80, with fines typically halved if settled promptly. However, certain councils, including the London boroughs of Islington and Westminster, have exercised powers to impose steeper fines of up to £110.
RAC senior policy officer Rod Dennis said: “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.”
Naturally, given the exceptional conditions currently being experienced across much of the UK, police officers and enforcement officials may opt to exercise a degree of leniency.
