"The National Union of Teachers (NUT) has written to schools throughout England and Wales telling them they could be in breach of employment law and health and safety regulations if they keep schools open during the pensions-related dispute.
"The letter emerged as Downing Street on Monday backed plans for parents to staff classrooms during the walkout, with ministers appearing increasingly determined to face down militant trade unions.
"David Cameron will make a last-ditch direct appeal to public sector workers today not to go on strike on Thursday, insisting their current pension arrangements are not fair to the taxpayer."