I lost gas to my ovens and discovered that it was because the automatic timer had inadvertently been set, i.e. because the timer was set to turn on at 16:00, then it prevented me turning the oven on manually before that. I cancelled the timer and all was well.
Some double ovens have solenoids fitted so if you have no electricity the ovens wont work (hobs dont have solenoid that is why they still work but probably wont ignite from spark (just use matches)