Apart from a few special-purpose authorities some of whose members are appointed by other local authorities, by Government, or, in the case of fire authorities, by insurance interests, members of local authorities are elected triennially, any qualified elector being eligible to seek election. In general the franchise extends to all persons aged 21 years or over who either possess a rating qualification or who, being British subjects, possess a residential qualification in the district of the local authority concerned. The right to vote for members of land drainage and river boards is, however, restricted to those who possess rating qualifications. Plural voting on the basis of the value of rateable property is permitted in elections for county councils and several types of special-purpose authorities. Where rabbit boards rate on the basis of livestock or acreage, plural voting is also permitted.