Conservative plans to create a network of "free" schools will take Britain back to the fragmented education system of the 19th century, when schools relied on wealthy benefactors, philanthropic organisations and the church, the NUT conference heard.
The warning came as the union declared it is to ramp up its campaign against the spread of academies and other forms of "independent" state school. It plans to do this by threatening industrial action and vigorous campaigns in affected areas.
A motion opposing the further establishment of academies and free schools claimed that the introduction of the "Swedish model" would represent a "radical extension of privatisation and de-regulation, threatening the fabric of the long fought-for national pay deals and even recognition of unions themselves".
Douglas Morgan, from the NUT in Birmingham, told delegates at the event in Liverpool: "What the Conservatives are offering us is a system we had in the 19th century."
Delegates also told several horror stories of academy schools refusing to allow union activity on campus, or teachers feeling so threatened by management that they had to meet their reps in parks and gloomy pubs.
The motion opposed the involvement of the private sector in education, from corporate sponsors for academies to companies bidding for Building Schools for the Future contracts.
It said: "The growth of academy chains, primary trusts and federations as a result of new government guidance poses a serious threat to democratically accountable education, and shows the potential for the establishment of a few competing, large national providers."
The joint winners of the Young Activist of the Year award given by teaching union the NASUWT said they were concerned about a potential future Conservative government. Paul Daly, a 28-year-old maths teacher at High Tunstall school in Hartlepool, received the prize for his work in an industrial action case and his support for the Love Music Hate Racism campaign. "I'm personally very scared about what's going to happen if the Conservatives win," he said. "Their policies are proven not to work."
Sarah Veater, a 25-year-old maths teacher at Witchford Village College in Cambridgeshire, agreed: "If the Conservatives win it will be to the detriment of the education system."