The circuit will work but you need to add two more resistors, one in series with the base of the BD438 so that you don't get a direct current path through it and the BC547 across the supply lines, the other from the collector of the BC547 to 12V+ to allow it to pass collector current and to ensure leakage doesn't turn the BD438 on. I suggest 10K from the BC547 to 12V+ and 1K in series with the BD438 base as starting values.