extend the crack and drive around for a curbside mowing crew. As i understand they had to have this kind of insurance, or the council will. Once you find one, drive past and then pull up suddenly, then walk back and complain that a rock from thier mower cracked your windscreen. Get their insurer details and go from there.
It's what i did. Apart from the having the crack in the first place. They really did break my glass. Replaced at no cost to me.

only problem was that the replacement glass didn't seem to have the tougher coating that the OEM stuff did and has tiny, tiny chips (from 2 x 2000Km road trips too!).