Your first call of action should be to telephone the gas emergency service on 0800 111 999 to rule out any safety or leakage issues (an engineer will normally attend within one hour of your phone call). Next, open every door and window to aerate the location with an immediate supply of fresh air. Then proceed with turning off the appliance and the main gas feed. Before reusing the appliance ensure it is checked by a “Gas Safe” qualified engineer. Do not smoke or turn on any lights or electrical appliances.