Nick Clegg's two years in office have convinced him that Britain's establishment is "broken" and "past its sell by date".
Clegg, who has faced criticism in the wake of declining poll numbers and local election setbacks, is expected to tell Parliament on Tuesday that Britain "is not broken at all", but will argue: "It is the British establishment that is broken. It is the institutions at the top that have let down the people.
The deputy prime minister is convening in a round table seminar with think tanks and democracy campaigners in Parliament on Tuesday.
The Liberal Democrat leader, who entered an historic coalition with the Conservatives in May 2010, will tell the group - expected to include the Electoral Reform Society, Unlock Democracy and 38 Degrees - he is more convinced than ever of the need to reform.
Opening the Portcullis House meeting, Mr Clegg is expected to say: "I have looked at the institutions of our establishment close up. And I can tell you, I am more determined than ever to see them change.
"Britain's broken establishment is now well past its 'sell by date'."
He will link the Parliamentary expenses scandal, the banking crash, party funding rows and the "sordid spectacle" of phone hacking.
"As political leaders, David Cameron, Ed Miliband and I all have to step up, and make sure we seize this moment.
"I really think if we can't tackle these deep problems in the established institutions of our country now, you'd have to wonder if we ever can.
"It is now or never. We have to show real courage."
And he will tell the group: "The economic crisis and political crisis aren't separate. They are part and parcel of a deep failure of our established institutions. You cannot build a healthy economy without strong, clean politics.
"Two years on I genuinely believe that we are at a critical moment. We are in the final stages of cross-party talks on party funding, we are about to publish a Bill for Lords Reform, we are enacting major reforms of our banking sector, and the Leveson Inquiry is opening a lid on politics, the media and the police. To leave this repair job half done, for me, is not enough.
"After two years in government, I'm even more determined than ever. We are at a critical, precious moment - we must seize it. I am more determined than ever to reform the broken institutions of this country. Unless, we do, we will never be the nation we could be.
"There is a better Britain bursting to escape the shackles of an old, tired, failed establishment."
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