Business secretary Vince Cable has signalled that the Liberal Democrats are willing to scrap the 50p tax rate, in exchange for a "mansion tax" on high value property.
Conservative MPs are pressing for the tax - levelled on earning above £150,000 - to be scrapped ahead of the Budget on 21 March.
Cable told the Today programme: "There is a broad understanding... that if the 50p rate were to go - and I and my colleagues are not ideologically wedded to the 50p tax rate... it should be replaced by taxation of wealth.
"The wealthy people in the country have got to pay their share, especially at times of economic difficulty.
"How exactly that's configured is a detailed matter for negotiation but that principle must be upheld, and a mansion tax is an economically very sensible way of doing it."
The current system meant vast numbers of "extraordinarily valuable" properties in the south of England netted very large gains for their owners, many of whom come from abroad, Cable added.
"You get people with multi-million-pound properties paying the same council tax as people in a three-bedroom semi, so the system doesn't work," he said.
Pain thresholds key
To communicate equity release's wider opportunities and benefits, writes Chris Flowers, providers and advisers need to think about how best to engage not only its usual target audience but also their families
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