The idea of a mansion tax was first proposed by the Lib Dems before the last election, although the Conservatives oppose the move and the policy was not adopted by the coalition government.
Conservatives are also expected to vote for this amendment - which will set out the areas of tax policy that the two parties agree on while not committing the coalition to the idea of a mansion tax before the next general election.
He said that the rumoured mansion tax would be a bad idea but increasing stamp duty on properties wroth is perfectly sensible because it gives the rich the freedom to choose.