Vince Cable has renewed the Liberal Democrats' demands for higher taxes on big properties as the price for agreeing to Conservative plans for a freeze in some state benefits in April.
In negotiations between the Coalition parties on George Osborne's autumn statement next month, Nick Clegg is pushing for the creation of two new council tax bands on homes worth more than £1m, as The Independent revealed last September.
The Chancellor is said to be open-minded but David Cameron is believed to be cautious about what has been dubbed a "backdoor mansion tax" which could alienate natural Tory voters.
Mr Cable, the Business Secretary, said yesterday: "There needs to be a sense of fairness, and these best-off people in society have got to contribute more. Property can't run off to Monaco and Liechtenstein. If you're trying to deal with abuse of the tax system, this is the best way of doing it."
Speaking on the BBC's Andrew Marr Show, Mr Cable condemned as "completely unacceptable" the "systematic abuse" of the tax system by multinationals including Starbucks and Google, accused of using overseas bases to limit their UK tax bills. He said more action was needed at international level, and Britain had to "beef up" its capacity to tackle tax abuse.