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Smell gas or fear carbon monoxide at night: what to do right now
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The short answer
0800 111 999: call the National Gas Emergency number immediately if you smell gas or think there is a leak. Open doors and windows, do not use switches, flames, smoking or appliances, and leave if the leak is in a cellar or basement.
Call the National Gas Emergency number on 0800 111 999 immediately. Call if you smell gas or think there could be a leak, at any time of the day or night.
What to do inside now
Open doors and windows to ventilate the property. You can turn off the gas at the mains tap, which is usually near the gas meter.
Do not turn any power or light switches on or off. Do not light any flame in the property, and do not use appliances that could cause a spark. Do not smoke or use naked flames.
If the gas leak is in a cellar or basement, do not enter. Evacuate the building instead. Do not enter a cellar even if your gas meter is in the cellar.
If you fear carbon monoxide
Carbon monoxide is colourless and does not smell. You cannot detect it by sight or smell.
Symptoms of carbon monoxide poisoning can include headache, dizziness, nausea or vomiting, weakness, tiredness, confusion, chest or muscle pain, shortness of breath, flushing and loss of vision. They may come and go, worsen in an affected building, and improve after leaving or going outside.
Do not re-enter
Do not go back into a property affected by carbon monoxide until you have medical or other appropriate advice.
If you have symptoms
Call NHS 111 if you think you have symptoms of carbon monoxide poisoning.
Related: Emergency numbers and essential services · Power cut in London · Electrical emergency at night
Sources
Every statement above rests on a page we opened and checked on 3 October 2026. We are not a medical, legal or emergency service: for an emergency, ring 999.
- NHS: nhs.uk/conditions/carbon-monoxide-poisoning/
- Cadent Gas (gas network): cadentgas.com/smell-gas
- SGN (gas network): sgn.co.uk/smellgas
Checked: 3 October 2026