How can I stop my Cannon Culinaire Cooker switching itself off?

My Culinaire gas cooker is sometimes difficult to light and you could say tempramental. When it is alight it will switch itself off in the middle of cooking so it's not possible to set the oven to come on automatically or leave it cooking without being supervised.

Any suggestions as to which part might be faulty.

Thanks

Model 11 132 38 White Serial Number 11 2 0001