Belling Cooker will not light fully?

One of the ovens on my Belling Country Classic (925GR)will not light properly. It ignites initially but usually after around 5 seconds it kicks in fully, now it just stays on the inital flame. I thought it might have been the gas safety switch but the other oven, grill and all the hobs still all work. Would there be an individual safety switch for one oven or is there another part that could be at fault? Thanks, Jamie