Schools, excluding independent schools, (meaning a school at which full-time education is provided for five or more pupils of school age - whether or not such education is also provided for pupils under or over that age, not being a public school, a grant-aided school or a self-governing school) may be used as polling stations free of charge, and the legislation allows you to require a room in such schools for use as a polling station.1
You are also entitled to use, free of charge, any publicly-funded room as a polling station.2
You will, however, need to pay for any lighting, heating, etc., costs incurred when using such rooms as polling stations.3
You should liaise with the relevant schools and managers of publicly funded rooms at the earliest opportunity to confirm that you want to use certain rooms within their premises as polling stations.