Scottish Gas workers have balloted for industrial action in a row that could lead to hundreds of staff going out on strike in a dispute over conditions.Centrica, which owns the utilities giant, last month said it could fire and rehire its entire UK-wide workforce of 20,000 if they didn’t agree to changes to their contracts.The firm - which has more than 1,000 workers based north of the Border - claimed such a bold move was only an "insurance policy" but issued statutory HR1 and s188 notices