It will be insured by police, the driver was arrested for being over the limit on a road side breathalyser, which would NOT affect your insurance until the static breathalyser is used in the station to determine if you are over the limit, then you will be either charged or released depending on outcome.
I still dont think it would affect the insurance pay out as it was in the care of the Police, who are insured to drive ANY vehicle so the police insurance would of kicked in the moment the plod, launched it down the road LOL