If you smell gas, phone National Grid Gas Emergencies 0800 111 999 (This is a 24 hour emergency line)
Open your windows and doors to let air in, make sure all gas appliances are turned off and turn the gas off at the mains if possible. Do not turn lights on or off and avoid using other electrical switches and appliances as this could trigger an explosion. Do not smoke, light a match or any other naked flame. Do not try and investigate the problem or attempt to fix a leak or a faulty appliance.