Theresa May's policy chief has said he is standing down from his role at No 10 to concentrate on grassroots reform of the Conservative Party.
George Freeman said an "ambitious" programme of party reform was needed to reconnect with younger voters in the wake of the Tories' "ill-conceived" general election campaign.
The Mid Norfolk MP was originally appointed to chair Mrs May's Policy Board when she became Prime Minister in July 2016.
Writing on the ConservativeHome website, he said he would now be focusing on his role as chairman of the Conservative Policy Forum - which aims to give a voice to grassroots members.
It is understood that the Policy Board, which was based in No 10, has not been reconstituted since the general election in June.
In his article, Mr Freeman said there needed to be a real commitment to learn the lessons of the election - which saw the Conservatives lose their overall Commons majority - and reverse the decline in membership numbers.
"Given the deepening disconnection between the Conservative Party and the new generation of aspirational voters under 45, the new intellectual battle of ideas reshaping our political landscape, this is now urgent," he said.
His comments follow the disclosure that he wrote to Mrs May in the run-up to the election warning that the Tories risked being seen as "a narrow party of nostalgia, hard Brexit, public sector austerity and lazy privilege".
For Labour, shadow cabinet office minister Jon Trickett said: "For a man who once said that the 'raison d'etre' of his role in Number 10 was to face the challenge of renewal in office, his resignation speaks volumes on the current state of the Tories in Government."