Abstract: An electrical circuit for connection to a high tension lead which is connected to a spark plug of a spark ignition internal cumbustion engine. The circuit comprises a capacitor (11) the capacitance of which is such that, if a high voltage pulse is applied to the high tension lead, the voltage developed across the capacitor and the charge stored by the capacitor are sufficient to initiate and sustain and ignition spark. The capacitor may be voltage dependent to achieve an optimised spark current characteristic. A resistor (12), such as a voltage dependent resistor, and a voltage controlled discharge device (13) may be connected in parallel with the capacitor.