Michael Gove is encouraging parents to break this week\'s mass teachers\' strike by volunteering to turn up and take lessons themselves, The Independent on Sunday has learnt. In an unprecedented step in relations between the Government and trade unions, the Secretary of State for Education said that classrooms threatened with closure could remain open if head teachers used the \"wider school community\" – including pupils\' parents – to teach lessons. Some head teachers have written to parents asking them to consider, if they have been vetted by the Criminal Records Bureau (CRB), volunteering to ensure lessons go ahead, Whitehall sources claimed yesterday. A spokesman for Mr Gove said the minister thought it was \"great\" if parents could help out with teaching. But the move triggered concern from the National Union of Teachers, whose members are among 750,000 teachers and other public sector workers walking out on Thursday in a dispute over major changes to public sector pension schemes. The NUT questioned how classes could go ahead because even CRB-checked parents would need to be supervised. The step suggests Mr Gove has pushed the concept of the Big Society to include strike-breaking. Ed Davey, the employment affairs minister, has also been accused of encouraging strike-breaking by declaring that the public would expect \"sensible contingency planning\" to take place. It came as ministers raised the fresh threat of new strike laws to crack down on future walkouts. It is understood that raising the legal threshold for turnout in a strike ballot is under active consideration. Turnout in the NUT strike ballot was 40 per cent, while for the Public and Commercial Services Union (PCS) ballot it was 32 per cent. Banning full-time union officials in the public sector from earning a taxpayer-funded wage is also on the table, ministerial sources said. \"We have ruled nothing out, although it would be a last resort,\" a source said. Whitehall officials said there was already \"anecdotal\" evidence of heads writing to parents asking them to teach this Thursday. Retired teachers are also being asked to volunteer. In a letter to schools last week, Mr Gove encouraged head teachers to use all necessary measures to keep schools open. He wrote that there was nothing to stop head teachers from dropping the national curriculum for a day or increasing the pupil-to-teacher ratio if it meant keeping the school open. He asked heads to consider \"the full range of local resources available to you from within your school staff and the wider school community to ensure that wherever possible your school remains open\". Asked whether \"wider school community\" meant getting parents to teach lessons, a spokesman for the minister said yesterday: \"It is up to schools how they want to keep themselves open. If they do that kind of thing, we think that is great.\" But Christine Blower, general secretary of the NUT, said: \"We are very sympathetic to the problems parents will have on the day. However, substituting CRB-checked parents for teachers won\'t work, as pupils simply won\'t be taught.\" Unison, which is not among the unions striking on Thursday but is planning \"rolling\" strikes later this year, has expressed support for the action by urging teaching assistants among its membership to resist being drafted in to cover lessons. Thousands of schools across England and Wales, mainly at primary level, are expected to close on Thursday as a result of the 24-hour co-ordinated stoppage. A survey of 18 local authorities by The IoS found an average of 37 per cent of schools will close on Thursday. Local union officials in Lancashire claimed all 580 schools in the county would be closed or partially closed, while 83 per cent in the Neath Port Talbot county council area are expected to shut. Besides the NUT and PCS, workers from the Association of Teachers and Lecturers and the University and College Union are striking over pensions. According to the J30 Strike website, more than 100 rallies, marches and pickets are planned across Britain to show support for the strikes, from George Square in Glasgow to Lemon Quay in Truro, Queens Road in Aberystwyth to Church Street in Dover.