I have a car with a large crack, 30cm or so, on the passenger side, not in the drivers main view. In fact I didn't notice it when driving the car in the car park. Does anyone know the rules on windscreen damage, and does damage on the passenger side matter?

Yes. As a rough rule anything within the area swept by the wipers is a no-no, but also any major crack anywhere will remove the structural integrity so it's an automatic fail.

Is the car insured? Is the screen usually covered under basic car insurance here?