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
No one gave him a chance when he announced his candidacy, but Donald Trump is just 166 days away from becoming US President.
German police are investigating an online picture thought to be of two British men doing a Nazi salute at a former concentration camp.
Late sunshine here and there this evening - but more cloud for southern Scotland, northern England and Northern Ireland again.