One of the burners ignition will not turn off - it continually is sparking - i have to turn off the elec supply to stop the ignition ? any ideas

Hi and welcome to FixYa, I am Kelly. On the burner your having problems with the ignition control switch located in front of the gas control vale on the stem has failed. These are cheesy little switches that are thin ceramic with nothing but 2 strips of copper inside them. One piece is fixed and the other piece is movable by the ceramic switch cam. If the movable copper arm or fixed copper strip gets bent the ignition will not shut off. Also if the ceramic cam of the switch fractures it will cause the switch to stay actuated. The gas valve has to be disconnected and removed to change the switch on most units. The wires in the switch have to be unlocked by inserting a jewelers screwdriver into the holes in the switch body to release the wires. These switches are common to most every gas cook top models no matter the brand. Without your model number I can not provide you with the manufacturers replacement part number. Change the burner ignition switch on the front of the gas valve for the burner with the problem and it will work fine.
Thanks for choosing FixYa,
Kelly