Justine Greening has attacked the Treasury for failing to properly fund education because it views it as a cost rather than an investment.

The former education secretary last year failed to secure new Treasury money for schools, instead having to find £1.3 billion from elsewhere in the DfE budget.

And this summer her successor Damian Hinds could not persuade chancellor Philip Hammond to fund the 2018-19 teacher pay award, and had to find £508 million from existing DfE resources.

Ms Greening told a fringe meeting at the Conservative Party conference today that the Treasury should plan for the long-term returns of investment in areas like early years literacy over a 10 to 20 year period.

She said: “But if you don’t properly value returns, you don’t invest in them properly. That’s the bottom line.”

Ms Greening said the Treasury, where she previously served as a minister, can put a value on infrastructure projects that could reduce congestion, “but it doesn’t put a value in the same way on educating our children better”.

She added: “It doesn’t have a framework properly for valuing investment in people, whether it’s health or education, whether it’s early intervention to help someone who is at risk avoid a life of crime and all the consequences of that for not just for them but for wider society.

“That’s not seen or accounted for as an investment.

“Instead, it’s always been seen by Treasury as a cost, and of course we always know that Treasury likes to manage costs down, yet human capital – people, our ability and capacity to do well – are at the centre of this country’s future success.”

She urged her party to make social mobility its “central driving mission” as it seeks to win its first landslide since 1987.

The Putney MP suggested that the government should expand the number of the flagship Opportunity Areas that she set up to improve social mobility from 12 to 120.

She said: “Those 12 Opportunity Areas should just be a start, not the sum total of our ambition for communities.

“Why not create at least 100 of them? If you look at the areas of our country that could do the best and are the furthest away from a level playing field, about 120 could become Opportunity Areas and could really benefit from that.”

Ms Greening suggested the tax system should be reformed in these areas to “overtly encourage and reward businesses who employ people to deliver more opportunity where it is most needed”.

She put forward the idea of the Treasury scrapping employers’ national insurance contributions in Opportunity Areas to reward employers who are already there, or move there.