Jeremy Corbyn is expected to say Theresa May’s flagship policy to create new grammar schools in England will be defeated by a concerted campaign by the Labour movement.



In a bullish speech to a private dinner at the TUC’s annual conference on Monday evening, he will say the plans show May is a deeply ideological prime minister and warn that her plans will play into the hands of her opponents.



He will say: “Just as we turned them back on forced academisation, together we will defeat their plans on grammar schools.”



The Labour leader will also say May has been hypocritical in claiming that she represents the many rather than the privileged few, given that she voted in favour of the bedroom tax and the trade union bill and now wants to segregate children at 11 years old.



Corbyn is favourite to beat Owen Smith in a Labour leadership election, the result of which will be announced on 24 September, but is known to be under pressure from some in the union movement to show he can take on the Tories.



Dave Prentis, the general secretary of Unison, the UK’s second biggest union, which backs his leadership, said on Sunday it was time for Labour to become an “electable” party.



At the general council dinner at the Grand hotel in Brighton, Corbyn will tell delegates that while May sets about restoring grammar schools, “she’s doing nothing about the cut in the schools budget, nothing about the teacher shortage, and nothing about rising class sizes.”



He will say: “This isn’t a matter just for the education unions – many of your members are parents, and we all have a stake in ensuring no child is left behind, that we have an education system and an economy that works for everyone. They are the values that guide us: unity and universality, not division and privilege.”

The grammar school plans announced by the prime minister last week were formally presented to parliament on Monday, launching a consultation process.



May has said the expansion of existing grammars and the opening of new selective schools will be accompanied by quotas to ensure poorer pupils are not excluded.



But teachers’ leaders and opposition parties have argued that increasing selection will undermine the standard of education available to the majority of pupils who will not get a place in a grammar school.



Several senior Tories have already voiced their opposition to the plans, raising questions over whether Tory whips will be able to force through legislation in the Commons.



Nicky Morgan, the former education secretary, said increasing academic selection would be “at best a distraction” and risked “undermining six years of progressive education reform”.



Morgan’s own flagship education policy, forcing all schools to become academies, was defeated this year by a rebellion by Conservative backbenchers.