How to de-ice your car safely on a frosty morning, and what the Highway Code requires before you set off

The short answer

Start the engine with the heater set to the windscreen, spray de-icer on the glass, and work round the car with a scraper while the cabin warms: windscreen, side windows, rear screen, mirrors, then the lights and both number plates. Do not pour hot water on the glass, do not leave the car running on the road while you go back indoors, and do not drive off through a porthole. The Highway Code says you MUST clear all snow and ice from all your windows and MUST ensure that lights are clean and number plates are clearly visible before you set off. Those are the rules with the force of law behind them, not advice.

The rules the Highway Code sets

Rule 229 covers the morning routine in four lines. You MUST be able to see, so clear all snow and ice from all your windows. You MUST ensure that lights are clean and number plates are clearly visible and legible. Make sure the mirrors are clear and the windows are demisted thoroughly. And remove any snow that might fall off into the path of other road users, which means the roof as well as the glass. Annex 6 of the Code adds that windscreens and windows MUST be kept clean and free from obstructions to vision at all times, and that before winter the washer bottle should carry an anti-freeze agent and the demisters, wipers and washers should all be working.

Rule 123 is the one people forget on a cold morning. You MUST NOT leave a parked vehicle unattended with the engine running, or leave the engine running unnecessarily while the car is stationary on a public road. Starting the car and going back inside for a coffee breaks that rule if the car is on the street, and an unattended running car with the keys in it is also the easiest car in the road to steal.

Step by step on the driveway

1. Engine on, heater to the screen, rear demister on. Set the fan high and the temperature warm, and switch on the air conditioning if you have it; it dries the air and clears mist faster. Stay with the car.
2. Spray before you scrape. De-icer softens the frost so the scraper slides rather than grinds. Give it a moment to work while you do the next step.
3. Lights and plates first. They take seconds and they are the ones you cannot see from the seat. Wipe both headlamps, the rear lamps and both number plates; the Code requires all of them clean.
4. Windscreen, then every other window. All of them, to the edges. Then both door mirrors and the camera lens if you have one.
5. Wipers last. Lift them free of the glass before you switch them on. A blade frozen to the screen tears when the motor pulls it, and a wiper that fails to clear the screen is an MOT item in its own right.
6. Wait for the mist to go. A clear outside and a fogged inside is still a car you cannot see out of. Drive off when the whole screen is clear, not when the hole is big enough.

Three things not to do

Hot water. Glass that is well below freezing and suddenly heated on one side can crack, and the water refreezes on the drive and on the wipers. Lukewarm water does less harm but still refreezes; de-icer and a scraper are the tools for the job.

The wrong scraper. A bank card, a CD case or a metal spatula will scratch the glass, and fine scratches catch low winter sun and oncoming headlights for the rest of the car's life. A plastic scraper costs little and lives in the door pocket.

The porthole. A cleared patch the size of a dinner plate hides pedestrians and cyclists at every junction, and it is the plainest breach of rule 229 there is. If you are short of time, the answer is to start five minutes earlier, not to drive half blind.

Set the car up once for the season

The Met Office's winter checklist is short. Top up the screenwash with a product rated to at least -15 degrees Celsius, because plain water freezes in the jets on the first cold morning and leaves you with a salted screen and nothing to clear it. Check every bulb and indicator and replace any that are out. Change wiper blades that smear or judder; the Met Office suggests once every 12 months. Check the coolant sits between the marks with the engine cold, and keep a scraper and a can of de-icer in the car, not in the garage. A battery that is slow to turn the engine on a mild morning will be slower on a cold one; have it tested before it lets you down.

If frost turns to fog, as this week's forecast suggests it may, the Code says you MUST use headlights when you cannot see for more than 100 metres, and the Met Office says to use dipped beam rather than main beam, which bounces back off the fog. Fog lights go off again as soon as visibility improves. Our fog driving piece has the rest.

What this does not mean

This article contains no statistics and makes no claim about any make or model. A clear car is the start of a safe journey, not a guarantee of one: the Code says stopping distances on ice can be ten times those on dry roads, and that on ice tyres make almost no noise, so the first warning you get may be the steering going light. If the roads are icy, drive slowly in as high a gear as you can, brake and accelerate gently, and leave far more room than feels natural. Where a Met Office warning covers your area, think about whether the journey needs making at all.

Sources and method

This article contains no MOT statistics. The rules are quoted from the Highway Code pages on GOV.UK and the checklist from the Met Office winter pages, as they read on 3 November 2026; the forecast referred to is the Met Office UK forecast issued at 04:00 that day. The MOT reliance notice below applies to the MOT history this site refers to elsewhere.

• GOV.UK: The Highway Code, driving in adverse weather conditions (rules 226 to 237)
• GOV.UK: The Highway Code, rules 103 to 158 (rule 123, engine running)
• GOV.UK: The Highway Code, Annex 6, vehicle maintenance, safety and security
• Met Office: six simple checks to prepare your vehicle for winter
• Met Office: advice for travelling in fog
• Met Office: UK weather warnings

This article is general information drawn from published test records. It is not professional, mechanical or legal advice, and an MOT pass or a clean MOT history does not guarantee that a car is roadworthy today. If you are unsure about a car, have it inspected by a qualified mechanic. You can check any vehicle's MOT history free on the official GOV.UK MOT history service.