Iain Duncan Smith suffered a new setback yesterday when it emerged that his director of strategy quit his post because he felt the Tory leader blocked the radical change the party needs to regain power.

Until three weeks ago, Dominic Cummings was expected to play a pivotal role at this week's Tory conference in Bournemouth. Instead, he will watch it on television.

Exactly why Mr Cummings, 30, walked out on Conservative Central Office after eight months has not been explained. He has refused interviews and turned down offers to write articles attacking his former boss. Although he would not comment yesterday, friends and Tory allies said he had lost confidence in Mr Duncan Smith after the leader rejected his ideas for sweeping reforms.

One ally said: "Dominic believes that centre-right parties need nothing short of a revolution, a complete transformation of how they operate. He feels those at the top of the party do not understand the scale of the problem they face and are incapable of taking the action necessary."

Mr Cummings' plan was blocked on the following issues:

* A complete revamp of the party's policies and policy-making machinery;

* An overhaul of the Tories' communications so that the party speaks to the voters in "a language they understand" and admits its past mistakes;

* Intervention by Central Office to raise the number of female parliamentary candidates.

"We needed a revolution on these three fronts, but all we got was tinkering," one supporter of Mr Cummings said.

Mr Cummings reportedly complained that the Tory party was "run by Parliamentary obsessives". One ally explained: "As the outside world became more hostile and Blair more difficult to grapple with, people just retreated into doing pointless things in Parliament. Spending 10, 20 or 30 years in Parliament is not a good schooling for adapting to the 21st century.

"The best way to exploit the lack of trust in New Labour is to adopt a completely different style. But we didn't have enough people capable of understanding that or doing it."

Although some modernising allies of Michael Portillo have portrayed Mr Cummings as a "Portillista", he is not. He has told friends that both the Portillo camp and his right-wing critics, led by Lord Tebbit, have "lost the plot".

Mr Cummings did not want the Tories to go "soft" on issues that appeal to their core voters. "If we talk about education, health, the vulnerable and poverty, that then enables us to go hard for Labour on crime, asylum, the euro and tax. But, crucially, it means that we are not defined by these traditional policies," one ally said. The aim was to get the best of both worlds, broadening the party's appeal while shoring up its core vote.

The criticism of Mr Duncan Smith will fuel doubts among Tory modernisers about whether he is the right leader for next general election. Mr Cummings believes privately that some Tory grandees are already discussing a plot to oust the party leader.