Gordon Brown and David Cameron have clashed over reform proposals which could see a new electoral system used in Westminster elections.
Speaking in the Commons, the prime minister left the door open to change but indicated it would not come before the next general election.
But David Cameron accused the government of trying to "fix the rules" as it becomes more unpopular.
He argued that the current system would maintain the link between one MP and their constituency, and allows "discredited governments" to be thrown out.
And the Tory leader said a completely proportional electoral system would have "massive drawbacks", as seen with the election of BNP members to the European Parliament.
In his responses, Brown said that the BNP's "politics of discrimination" have "no part to play" in British politics.
But he noted that the proposed 'alternative vote plus' system of electoral reform would prevent the BNP from being elected.
And the prime minister said Cameron was approaching the issue with "an element of self interest".
The clashes came ahead of Brown's statement on proposals for 'democratic renewal'.
The prime minister told MPs: "The last few weeks have shown us that the public require - as an urgent imperative - higher standards of financial conduct from all people in public life and an end to the abuses of the past.
"There is no more pressing task for this Parliament than to respond to this public demand."
His proposals included plans for a new statutory regulator of Parliament, which will oversee allowances, maintain the register of interests and ensure efficiency and value for money in parliamentary expenditure.
Noting that the last expulsion of an MP had been 55 years ago, the prime minister backed a new code of conduct for MPs to be included in fresh legislation.
"The sanctions available against financial misconduct or corruption have not been updated to meet the needs of the times," he said.
"This is not a modern and accountable system that puts the interests of constituents first. It needs to change."
The Senior Salaries Review Body will also examine the system of financial support in the House of Lords.
Separately, there will be a review of ways in which accountability to Parliament can be boosted, including greater powers for select committees and allowing more time for non-government business.
The scope of the Freedom of Information Act could also be extended to cover other bodies which spend public money.
And the time before official documents are released will be cut from 30 years to 20, while Sir Tim Berners-Lee will lead a review of ways in which government data can be opened up through the internet.
Brown also pledged fresh efforts to ensure the public remains engaged with the political process.
He said that reform of the House of Lords will "move forward", with final stage of proposals to be detailed before the summer recess.
On plans for a Bill of Rights and Responsibilities, the prime minister said: "I personally favour a written constitution."
He also detailed plans for more devolution, including policing and justice issue in Northern Ireland and greater public involvement in community decisions.
Addressing the controversial issue of electoral reform, Brown said there would be change only if there is a "broad consensus".
The government is to "set out proposals for taking this debate forward", while the door was also left open to lowering the voting age to 16.
"In the midst of all the rancour and recrimination, let us seize the moment to lift our politics to a higher standard," said Brown.
"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."
Responding to the statement, Cameron said that the "real change we need" is a general election.
He noted that there is "much we support" in the proposals, but said the prime minister "has promised constitutional reform countless times before". "Why has it taken so long?" he asked.
Setting out additional proposals, the Conservative leader said the public should be able to stop excessive rises in local taxes.
And he warned that proportional representation was "a recipe for weak coalition government" with power moving to party managers making "backroom deals".
He also said the Boundary Commission should redraw boundaries to make constituencies the same size, while the number of MPs should be reduced.
Cameron added that the proposals were a "sorry attempt to distract attention away from a government that has lost its authority".


Have your say...
Please enter your comments below.