Parents and grandparents will be allowed to draw on their pension pots to secure deposits for young family members in a bid to boost home ownership, Nick Clegg said.
The Deputy Prime Minister said detailed proposals were being drawn up by Liberal Democrat ministers as part of efforts to make the economy "fairer".
But he also declined to commit to pushing for any specific wealth tax despite promising activists at the party conference that he would play hardball with the Tories on the issue.
Speaking on BBC1's Andrew Marr Show from the Brighton gathering, he said: "This is part and parcel of something which I think most people agree with which is that as we fill in the black hole in the public finances we have also got to make sure that we do not put Humpty Dumpty back together again and make the same mistakes, that we re-wire the British economy and make it fairer and give people more opportunities.
"Let me give you one very good example: we have thousands of young people who are desperate to get their feet on the first rung of the property ladder but deposits have doubled and the number of young people asking for help from family members has doubled.
"So I can announce today that the Government is going to do something that hasn't happened before: we are going to work out ways in which parents and grandparents who want to help their children and grandchildren buy a property of their own, we are going to allow those parents and grandparents to act as a guarantee if you like so their youngsters ... can take out a deposit and buy a home.