I have a Gas oven issue?

Situation: I hold the knob down of the oven on gas mark 7 lets say; the oven become alight i hold down for 30seconds then let goes of the oven knob the fire goes out! any suggestions of what part is broken and need replacing?

I had same gas oven issue like you. One of my friends recommend me this company http://www.ovenspares.com.au and they solved my problem after that i don't face this problem. That's why i also recommend you this company to fix the problem.