Nick Clegg is set to rule out the possibility of the Government's new free schools being run for profit as he seeks to reassure Liberal Democrat sceptics that the policy will improve social mobility.
As the first wave of the new-style schools prepare to open this week, the Deputy Prime Minister will insist that he would "never tolerate" them becoming "the preserve of the privileged few".
In a speech, he will say that they will be incentivised to attract under-privileged pupils and set up in areas of high deprivation or with shortages of school places.
The free schools policy is seen as a distinctly Tory strand of the Coalition Agreement, with Lib Dem activists voting against it at their party conference last year over concerns that it is socially divisive.
Mr Clegg will acknowledge that the programme - in which groups of parents, charities or any other organisation can bid to open schools where existing provision is poor - is "controversial" and carries "risks".
But he will go on: "I am confident we have mitigated those risks to make sure this is now a policy which will promote higher standards, better integration and fairer chances especially for children from the most deprived backgrounds.
"They must not be the preserve of the privileged few - creaming off the best pupils while leaving the rest to fend for themselves, causing problems for and draining resources from other nearby schools. So let me give you my reassurance - I would never tolerate that."
Tory Education Secretary Michael Gove, who has championed the flagship schools policy said on Sunday only that it did not need profit "at the moment". Asked about in the future, Mr Gove added: "Well we're in a coalition now and we're working to ensure that we get more free schools."
The first 24 free schools are planning to open within the next month. The Department for Education (DfE) said 15 of them were oversubscribed for their first year. Half of them are in the 30% most deprived communities, according to DfE analysis.
Mr Clegg will say that he wants to see all of the next wave of free schools - to be decided by Mr Gove in the next few weeks - to be in poorer neighbourhoods or in areas with shortages of places.