I wouldn't expect a random Letting Agent to have that information at their fingertips for every rented house they are involved with. The rule-of-thumb is that there is a gas isolation valve next to your gas meter.
Yes, you should have ignited the gas ring to use up the escaping gas until you could find a way to turn it off. It must be an old gas cooker, because those manufactured over the last 5 years commonly have a FMS (Flame Management System) which uses thermocouples near the gas outlets to monitor the temperatures there and turn the gas supply off if the flame goes out (or if the flame doesn't comes on after a few seconds).
The Landlord should know and his/her designated HMO Manager should know (the Letting Agent is not automatically the latter). Yes, the tenants should know where the gas isolation valve is and have easy access to it in order to turn it off in an emergency. Obviously, it is very much in the Landlord's interest that the tenants know this to avoid a fire/gas explosion and potential manslaughter charges if negligence is subsequently proven. The Landlord/HMO Manager should do a short Fire Safety course with all of their tenants every year to ensure the emergency procedures/fire extinguisher operating protocols etc are understood by everyone.
Yes, that is standard practice. A Council HMO inspector would advise that this is done.
Something similar happened in a HMO I rented a room in once. Not because of the gas cooker failing but because a drunk student came in at 2 AM, heated up some soup on a gas ring to eat before going to bed, but forgot to turn the gas ring off and went to bed. The flame blew out because she left the window open and in the morning when we came down for breakfast the kitchen reeked of gas. I had to tell everyone not to turn on any lights, use any electrical appliances etc and open all the doors and windows to get rid of the gas. Of course, they all blamed me, not her for the inconvenience!
They should at least replace the old gas cooker with a new one that has a FMS on it. If they don't do this complain to your Council's HMO department. Old gas cookers often fail the GSC (Gas Safety Certificate) inspection because their oven usually releases too much Carbon Monoxide. You might want to check the Gas Safety Certificates for the last few years to see if they have ever had the CO levels produced by it checked.
The landlord has already failed in his legal duties by not giving you access to the gas isolation valve for emergencies. Your gas cooker sounds very dodgy too. My last gas cooker failed its GSC after less than 4 years of use (CO production by the oven due to tenants never cleaning it out).
Yes, there are alarms which can detect gas, but the gas cooker definitely should be replaced with a modern FMS one so they should not be necessary. Do you have Carbon Monoxide detectors in every room with a gas appliance and on every floor of the HMO? Because they are a legal requirement too.
