A chemical odourant is added to natural gas to give it a distinctive smell and make it easy to detect gas leaks.

If you smell gas indoors...

Never look for a gas leak with a flame.

It may not be a gas leak. People sometimes accidentally leave gas cooker burners turned on and unlit, and this may be the cause of the gas smell. Also check that any heaters have been properly lit. Turn the burner off and wait until you can no longer smell the gas before trying to use a gas appliance.

Open doors and windows. Don't operate power or light switches, don't turn electrical appliances on or off, and don't use your telephone, as they might spark and create a fire. In particular, don't use a fan to provide ventilation.

If burners haven't accidentally been left on, leave the premises and turn off the gas at the meter. If safe to do so, switch off the power at the fuse box so that electrical appliances can't operate and generate a spark.

Call a licensed gas fitter or the gas supplier from a neighbour's telephone - it may be unsafe to use your own phone if gas is present nearby. Don't go back into your house until the gas supply is turned off at the meter and the smell of gas has cleared.

If you smell gas outdoors...

If you can smell gas outdoors, don't try to find the leak yourself - turn off the gas supply at the meter, and call your gas supplier immediately.