If you can smell gas, think you have a gas leak, or are worried about carbon monoxide.
Go outside, call the National Gas Emergency line onto report this. The line is open 24 hours a day, 7 days a week. They'll advise you with the next best actions.
You won't be charged for any checks or repairs to your gas supply or meter.
To stay safe:
Open all windows and doors to get rid of the gas
Turn the gas off if you've left it on, or the pilot light has gone out
Turn the main gas tap to 'OFF' (your supply is off when the ridged line on the spindle is across the pipe)
Smoke or light matches
Turn electrical switches on or off
Wait for someone else to call the National Gas Emergency line - you could be putting yourself or others at risk.
Don't go back inside until the National Gas Emergency Service has given the all clear.