The party said a 0.5% increase on property tax for the most wealthy could help support tax breaks for those on lower incomes.
Lib Dem Leader Nick Clegg (pictured) said such a move could better four million low earners and raise the starting tax threshold from £6,500 to £10,000.
Speaking from his party's Bournemouth conference, Mr Clegg described the hike as no "big sacrifice"
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"It is a perfectly reasonable thing to ask of people who have got properties of that value, and it's completely in line with how pretty well every tax system in the world works," he told the Independent.
Mr Clegg has come under fire from party members after mooting a possible shift in Lib Dem university fees policy.
He hinted that the party may scrap its plans to axe fees due to the economic downturn.
Lib Dem Treasury spokesman Vince Cable has supported the tax move.
He said it was unfair homes that worth £30m were taxed the same amount as those valued 30 to 40 times less.
"We have seen the super-rich pouring their money not into job creating businesses but into acquiring mansions," said Mr Cable.
The policy would put a £2,500 charge on homes worth £1.5m and £15,000 for a £4m property.
(PR/KMcA)
