Many household appliances are supplied by gas and they can occasionally leak. If your home does suffer a gas leak you should be able to smell it first but if you don't and you start to have dizziness, fatigue, nausea, headaches and irregular breathing when you are inside but not outside it may be because of a gas leak, seek medical attention or call NHS direct for advice.
CALL 0900 111 999 open 365 days 24 hours a dayDON'T create a flame and put out any naked flames.DON'T smoke DON'T attempt to repair or fix the suspected leakDON'T operate electrical switches.OPEN doors and windows to ventilate the area.KEEP people away from the area.TURN OFF the gas at the control valve.
Sources: hse and the national grid and gas safe guide