Tony Blair has defended himself against Tory charges that he "ripped up the constitution in a matter of hours" in last week's controversial cabinet reshuffle.
Mr Blair faced MPs in the Commons
The prime minister told MPs the shake-up represented "essential acts of constitutional modernisation" which would eventually be welcomed.
The changes will abolish the post of lord chancellor, downgrade the roles of Welsh and Scottish secretaries and create a new constitutional affairs department.
Tory leader Iain Duncan Smith accused Mr Blair of treating the constitution like his "personal plaything" in what was "the most botched, bungled and damaged reshuffle in modern times".
But the prime minister said it was right to axe the post of lord chancellor and end the "anomalous" position which meant a cabinet minister was in charge of appointing judges.
And in a Commons statement to MPs, he promised there would be "extensive consultation" about the changes which ushered in a new constitutional affairs department.
The plans will be published within the next few weeks, with parliamentary legislation to follow, he said.
Mr Blair claimed it "said a lot about the Tory Party" that they favoured a lord chancellor wearing 18th century breeches and women's tights, sitting on a woolsack, rather than running the courts service.
He said civil servants in the Scotland Office and Wales Office would report to the new constitutional affairs department because, after devolution, there was no longer a requirement to have separate Welsh and Scotland secretaries.
And he confirmed that the lord chancellor's role as speaker in the House of Lords would end, saying having a government-appointed minister in the role was "virtually unique" in any democracy.
But in heated exchanges, Mr Duncan Smith said the consultation process outlined by Mr Blair was irrelevant.
"Today is a humiliation for the prime minister," he said. "Today he stood up and tried to justify the decision made last Thursday by saying this is all just a
"The fact is he has already made up his mind."
"He used his reshuffle to charge headlong to change for change's sake."
The shake-up had been determined by "in-fighting" in the cabinet, he added.
"Last week the prime minister ripped up the constitution in a
matter of hours without consultation - as though our constitution was the prime
minister's personal plaything," he said.
Earlier, Home Secretary David Blunkett admitted that the presentation of the changes had not been handled well although he defended the principle behind the reforms.
"If you ask me was the presentation as good as we would have wished, the answer is no," he said.
Mr Blair's statement came after Commons speaker Michael Martin responded to Tory demands for the prime minister to explain the changes to MPs.
Downing Street said the prime minister was "relaxed" and "more than happy" to explain the constitutional changes to MPs in the statement which will follow prime minister's questions.
But Mr Duncan Smith said the Commons speaker deserved credit for "forcing" Mr Blair to make the statement.
Liberal Democrat leader Charles Kennedy said the government should have created a department of the nation and regions rather than merge the Welsh and Scotland offices into the new ministry.
And he said the creation of a supreme court was welcome, but did not go far enough.
He added: "If we had a greater and more sensible level of consultation, could
we not have avoided some of the difficulties of the last few days?"