When you depress the knob to ignite the fire, a microswitch in the gas valve is 'made' and initiates the operation of the electronic igniter. The contacts of the microswitch should 'break' when the fire is turned off. It may be that contacts of the microswitch are remaining closed when the fire is turned off such that the igniter continues to operate. The microswitch is not easy to access as it is underneath the plastic cap on the gas valve. It is probably advisable to have aa Approved workshop to look at this.
The lack of gas to the cooker may be caused by the fact that the glass lid has not been fully opened. There is an interlock that prevents the flow of gas if the lid is not fully open.