Gordon Brown today committed Labour to introducing fixed-term parliaments under sweeping constitutional reforms.
However, the Prime Minister did not set a date on when they would be introduced if Labour wins the election.
His promise came in a speech which was billed as painting himself as a constitutional moderniser who is open for business to do a deal with the Liberal Democrats in a hung Parliament.
"In order to reassure people, in this new century, that the executive will no longer be able to determine when it should put
itself forward for the people's approval, Labour's manifesto will include a new commitment to fixed term Parliaments," he said.
His critics, though, have repeatedly accused the Prime Minister of making repeated pledges on constitutional reforms but failing to deliver them.
Labour is proposing to consult during the next parliament to bring in fixed terms afterwards.
If Labour wins the election, it would hold a referendum in autumn next year on using alternative vote. A fully elected House of Lords would be phased in over a period of three general elections.
MPs would have to get approval for second jobs outside Parliament and they would be banned from working for lobbying companies.
Voters would also get the right to "recall" MPs if they commit gross misconduct and Parliament failed to take proper disciplinary steps.
Under "longer term" reforms, Labour committed itself to fixed-term parliaments and to "chartering" a course to a written constitution.
Labour is also proposing to strengthen Parliament by allowing people to trigger debates through petitions and for select committee chairs to be elected by secret ballots.
Opposition MPs, though, raised doubts over Mr Brown's promises.
Mr Brown's constitutional overhaul was seen as an olive branch to the Lib-Dems but Mr Clegg today tore into both Labour and the Tories, accusing them of blocking deals on party funding, lobbying and reform to the Lords.
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"Believing any promises from them on political reform is a bit like accepting a consumer service guarantee from Del Boy," he said.
He said Britain's political system was "corrupt" and even less democratic than Hong Kong in some respects.
But he kept open the door for a deal with Mr Brown, as well as Mr Cameron, in a hung parliament. Mr Clegg said the party which had the biggest mandate from the British people, "regardless of who leads it", had a moral right to seek to establish a government by its own or with other parties.
He stressed that his party would be "guided" in a hung parliament by four key policies. They are major tax reforms, a constitutional shake-up, more educational support for children, particularly from deprived communities, and a greener economy less dependent on the City.
Mr Clegg also toughened his party's line on the euro, saying it would not be right for Britain now.
On the Tory recall plans, shadow Commons leader Sir George Young said: "People want change and politicians must become more directly accountable for their actions."
