Michael Gove has endorsed Rishi Sunak to be the next prime minister as he accused rival Liz Truss of taking a "holiday from reality" with her tax plans.
The former cabinet minister, who was sacked by Boris Johnson, suggested Ms Truss's proposals would put "the stock options of FTSE 100 executives" before the nation's poorest people.
He added that he does not expect to return to frontline politics, as he backed Mr Sunak - the self-styled "underdog" in the race to replace the outgoing prime minister.
Writing in the Times, as polling of Tory members gives Ms Truss a clear lead, Mr Gove said: "I do not expect to be in government again.
"But it was the privilege of my life to spend 11 years in the cabinet under three prime ministers. I know what the job requires. And Rishi has it."
Mr Gove, who first backed Kemi Badenoch for the top job, praised Ms Truss for being "tenacious" and "brave", but said: "My heart inclined me to vote for Rishi".
"Liz has been admirably clear, consistent and principled in the case she has made. She's made her winning argument with winning brio," he added.
"But I do not think her prospectus is the right answer to the world we face. It does not address the fundamental problems of potential neglected, productivity suppressed and the vulnerable suffering the most."
Taking aim at her economic proposals, Mr Gove went on: "Here I am deeply concerned that the framing of the leadership debate by many has been a holiday from reality.
"The answer to the cost of living crisis cannot be simply to reject further 'handouts' and cut tax."
"I cannot see how safeguarding the stock options of FTSE 100 executives should ever take precedence over supporting the poorest in our society, but at a time of want it cannot be the right priority."
Welcoming his backing, a spokeswoman for Mr Sunak's campaign said: "Delighted to have the support of a party and cabinet veteran who has intellectual heft and shown the radical reforming zeal in every job he had, that we now so desperately need."
During the contest, Ms Truss has set out multi-billion pound plans to reverse the national insurance hike, temporarily suspend the green levy on energy bills and also scrap a planned rise in corporation tax.
At the party hustings in Manchester on Friday night, Ms Truss reiterated her plan to lift the ban on new grammar schools, saying she wants everyone "right across the country" to have the choice to enlist their children at them.
But Mr Gove highlighted the grammar schools pledge, when there is "neither the money to build them nor the evidence they advance social mobility", as among her plans that should not be among the Conservatives' priorities.
