Theresa May’s policy chief is standing down to concentrate on boosting the Conservative Party’s campaigning strength and appeal to younger voters.
George Freeman said the party needed to change after its “ill-conceived” general election campaign.
He warned the PM during the campaign that they risked becoming “a narrow party of nostalgia, hard Brexit, public sector austerity and lazy privilege”.
Labour said his resignation “speaks volumes” about the state of the Tories.
Mr Freeman was originally made chairman of Mrs May’s policy board when she became prime minister in July 2016.
The board was a small group of advisers set up to encourage “fresh thinking” in key policy areas, such as affordable housing. It has not met since the general election.
Writing on the ConservativeHome website, the Mid Norfolk MP said he would now be focusing on his role as chairman of the Conservative Policy Forum, which was set up in 2011 to give ordinary members more of a say.
In his article, Mr Freeman said he wanted to address falling membership and the “urgent” threat of “a rejuvenated Labour Party” by instigating a “bold programme of Conservative Party renewal”.
This would mean a new party chairman and team at party headquarters to “oversee the intellectual, organisational and cultural renaissance of a conservatism fit to shape and lead us through the 21st Century”.
“Given the deepening disconnection between the Conservative Party, the new generation of aspirational voters under 45 and the new intellectual battle of ideas reshaping our political landscape, this is now urgent,” he added.
He said the party had not yet “framed a coherent economic programme to tackle the underlying economic causes of the injustices which so many voted against in the election” but warned against becoming “Corbyn-lite”, which would only risk “tempting voters to vote for the real thing”.
Labour’s shadow cabinet office minister Jon Trickett said: “For a man who once said that the ‘raison d’etre’ of his role in No 10 was to face the challenge of renewal in office, his resignation speaks volumes on the current state of the Tories in government.
“He has caught the essence of the Conservative Party in a two-word phrase: lazy privilege.”