When the Vehicle is SORN it doesnt need to be insured , in the classic car world they do a " laid up insurance "
I guess it depends on the value of the vehicle, if its not the highest value, its got to be worth the risk, i know i would park my C1 on my drive and risk it, as it is only worth £1500, but i certainly wouldnt leave my VW splitty on the drive uninsured ( though it spent a few years in my garage uninsured a few years back )