Gordon Brown explains why he is proposing constitutional change
Prime Minister Gordon Brown has set out wide-ranging proposals to "clean up" and modernise British politics in an effort to reassert his authority.
He promised a consultation on changing the voting system - but he said there were "no plans" for a referendum on this issue before the next election.
He also pledged tougher sanctions for MPs guilty of misconduct, including the power for constituents to recall MPs.
Tory leader David Cameron said the "real change" needed was an election.
And he accused Mr Brown of trying to "fix" the electoral system in his party's favour by scrapping the current first-past-the-post system, which allowed voters to get rid of "weak, divided and incompetent governments and that is what we should be doing now".
He said proportional representation was a "recipe for weak coalition governments" and Mr Brown had only started talking about it "because he fears he is going to lose".
Lib Dem leader Nick Clegg - whose party has long argued for electoral reform - welcomed Mr Brown's "deathbed conversion" to the cause "from the man who has blocked change at every opportunity for the last 12 years".
The SNP and Plaid Cymru are to hold a debate on calling a general election now, backed by the Tories and Lib Dems.
But Justice Secretary Jack Straw said the scandal about MP expenses has increased the public's appetite for further constitutional change.
He told the BBC News channel: "The responsibility of this House of Commons, of the people in the House of Commons, is to sort out the expenses scandal first.
"It's completely disingenuous of David Cameron to say have a general election - that will sort it out. It won't sort it out at all. It's a precondition of having a general election to sort it out."
Mr Brown made his statement to MPs on constitutional reform as he seeks to regain the political initiative after a week of turmoil.
'Seize the moment'
In his statement, Mr Brown confirmed plans for a new independent Parliamentary standards authority and a new bill to be introduced before MPs break up for the summer recess setting out a legally binding code of conduct for MPs.
This would set out what the public could expect from their MPs and make it easier to expel those who misbehaved.
David Cameron accuses Gordon Brown of trying to "fix" the electoral system
He also pledged a crackdown on misconduct in the House of Lords and vowed to press ahead with democratic reform of the Upper Chamber and he promised to give urgent consideration to lowering the voting age.
He said Labour MP Tony Wright, chair of the public administration committee, would work with a cross-party Parliamentary commission to discuss constitutional reform.
This will look at other reforms such as making select committees "more democratic" and a mechanism to allow the subjects of petitions handed in to Downing Street to be debated in the House.
He also pledged to consult on extending Freedom of Information laws to bodies spending public money that were not currently covered by it and said official papers would be published after 20 rather than the current 30 years - excluding Cabinet papers and material relating to the Royal Family.
A review headed by Daily Mail editor Paul Dacre recommended lifting the veil of secrecy after 15 years.
In the midst of all the rancour and recrimination, let us seize the moment to lift our politics to a higher standard
Mr Brown repeated his commitment to consult on a written constitution - something he said he personally supported - and House of Lords reform.
He told MPs: "In the midst of all the rancour and recrimination, let us seize the moment to lift our politics to a higher standard.
"In the midst of doubt, let us revive confidence. Let us stand together because on this at least I think we all agree: that Britain deserves a political system equal to the hopes and character of our people.
"Let us differ on policy; that is inevitable. But let us stand together for integrity and democracy; that is now more essential than ever."
Tory leader David Cameron said he supported some of the proposed measures such as a Parliamentary standards authority and more power for local government.
But he repeated his call for unelected regional quangos to be scrapped and the number of MPs to be cut.
'Prepared to do it'
He said Mr Brown had promised constitutional change before and "nothing ever happens" and his current enthusiasm for it was merely a "relaunch distraction strategy" designed to get Mr Brown out of trouble.
Mr Cameron said a Tory government would introduce true reforms such as referendums on council tax increases and the "right of initiative" - allowing voters to propose new laws.
Just to be clear: the prime minister's statement will not - and was never going to - endorse a change of voting system nor any particular system
He also called on the PM to back select committee elections to end the power of prime ministerial "patronage", adding: "I am prepared to do it, is he prepared to do it?".
Lib Dem leader Nick Clegg said he welcomed many of the changes proposed by Mr Brown but said they had to be put in place before the next general election rather to put out to yet more committees.
Anything else would be a "betrayal of the British people who are angry and demanding that we change the rotten way we do politics for good," added the Lib Dem leader.
On electoral reform, Mr Brown said he did not favour proportional representation for Westminster elections as he did not want to break the link between MPs and constituencies.
But he said a debate on whether the vote system should change.
Ministers are thought to have discussed an "alternative vote" system to replace the current first-past-the-post method.
Campaign group Unlock Democracy said they welcomed Mr Brown's "rhetoric" on constitutional reform but it was no substitute for action.
Unlock Democracy director Alexandra Runswick said: "This afternoon, Gordon Brown was reduced to performing the role of a bingo caller, listing a whole series of potential reforms yet offering almost nothing of substance."
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