Danny Alexander has said no-one should face a cut in state help if no suitable smaller property is available and all disabled claimants should be exempt.
In a direct message to the Conservative government, the Chief Secretary to the Treasury said the Liberal Democrats will "make the case for these new fairer rules."
Speaking to The Mirror he said: "If we can't convince our Conservative coalition partners, we will commit to these reforms in our 2015 manifesto."
More top news
Heading to Wimbledon? Here's the forecast for the rest of the week.
The Scottish golf club plans to hold another vote on female membership just weeks after its members rejected the proposals.
George Osborne has said the UK economy is "prepared for the unexpected". So did he overstate his Brexit warnings?