Cannon Chester Gas cooker - my lower oven igniter wont stop clicking!!! ?

Does anyone know what is wrong with my Cannon Chester Gas Cooker. When i turn the lower oven on the igniter automatically kicks in, the trouble is after the inital pilot flame has been lit, the igniter wont stop clicking. Can anyone help. One of the lads from work told me to clean the probe at the back of the oven but that looks clean. Any advice would be gratefully recieved.