Zanussi Lindo 300 dryer will only run with half a load.

Most heavier duty electric motors like those in dryers and air conditioners have a motor start capacitor. This capacitor stores up extra energy to boost the normal current going to the motor in order to meet the heavier demand of starting up from a stop. If the start capacitor is bad, the motor will have trouble starting, but if given a hand, or needing less load as you describe, but will run fine once it gets moving.

You'll need to trace the wires from the motor to locate the capacitor; it may be combined with the motor's run capacitor or it could be separate. As long as you're in there I'd probably consider replacing both if they're separate.