When I switch on my Beko gas oven it lights up but then goes out?

My Beko gas cooker is over 8 years old and has been very good. But just yesterday, when I switched the oven on by turning the regulo to 6 or more and pressing the button, the flames will not stay on. It lights up ok, but as soon as I remove my finger, it goes out. Have never had this before Ms So I left it for a day, but the same thing happened. Now I can't use the oven, I'm stuck.