Mori,
At the moment, you cannot have an insurance policy which covers you for driving at weekends only. You will either have to get
temporary insurance every time you drive at weekends, sign up for
pay per month insurance or get the traditional annual car insurance and specify that you will be doing really really low mileage.
There used to be a
Pay As You Drive insurance before which would have allowed you to drive whenever you want, in your case weekends only, but this has been withdrawn from the market now.