Michael Howard has dismissed growing calls for him to stand down early as Conservative leader.
Howard: Sticking to timetable
In a letter to MPs, Mr Howard admitted plans for reforming the party "could have been better handled".
But he said it would not be in the party's interests to plunge it into an immediate leadership election.
A major contributor to the Tory party Sir Tom Cowie told the BBC's Newsnight programme on Thursday that Mr Howard should go "in hours or days".
'No early resignation'
Mr Cowie - a transport tycoon who contributed £400,000 to the Tories in the first fortnight of the general election campaign - said the party needed to "get back to the old race".
Earlier, ex-Tory chairman Lord Tebbit said Mr Howard should be replaced by the end of the summer so his successor could lead the Tory conference.
Some Tory MPs have said they are angry that proposals to reform the party and change how its leader is elected have been presented as a fait accompli.
And there is talk of signatures being gathered at Westminster to trigger an early leadership contest.
The proposed new leadership system would return the final decision to MPs, with grassroots members showing their views in a vote of local Tory association chairmen.
In his letter, Mr Howard said there would be two different votes, one on the leadership rules and one on constitutional reforms.
But both votes would take place at the meeting of the party's national convention, which includes 900 local Tory chairmen, on 27 September.
Mr Howard again promised there would be full consultation on the plans, with backbenchers able to discuss the package at a series of meetings.
He said: "I know it has been suggested by some people that we should hold an early leadership election.
"I do not believe that this would be in the best interests of our Party. Both before and immediately after the general election I was urged from all sides not to plunge our Party into an immediate leadership election."
Promising to stick to plans to hold the leadership election after the autumn Tory conference, he added: "I do not, therefore, intend to resign the leadership at an earlier date."
Tory MP Quentin Davies, who fears his party faces six months of "paralysis" before a new leader is chosen, reacted angrily to the letter.
He said: "It doesn't even begin to address the issues...
"We have got to make sure we get a new leader in place as soon as we responsibly can and certainly in advance of the party conference other wise frankly I can't see the point of having a party conference."
Mr Davies argued the party should change the leadership election rules urgently and leave the other reforms until later.
Earlier, Lord Tebbit said he thought it was right that MPs should choose the next party leader.
But he argued constituency associations should be allowed to decide who they wanted to run for Parliament.
He contrasted the Conservative failures at the past three elections with Marks and Spencer "no longer dominating the high street".
"This last election was the third one lost by John Major because it was while he was on watch that the party lost its reputation for economic competence," he said.
On Tuesday, Mr Howard briefed the 1922 Committee of backbench Conservatives over the plans, in what some MPs said resulted in a "fiery and angry" meeting.
Tory MP Bill Cash on Thursday said: "This party rule change has been a complete mess and there was considerable concern and anger about the lack of consultation and the way in which it was done."