How can I fix the safety catch on my Kenwood Prospero?

Sometimes my Kenwood Prospero won't start. I'm pretty sure it's failing to release the safety catch when the top is put down. Sometimes a bit of jiggling will fix it. I know there are two other safety catches on the top to make sure that the blender or food processor are in right when in use. Is there a similar one for when the main top of the machine is down? Can anyone tell me where to find it - have opened up the top to look myself and can't see anything obvious...