Nick Clegg has called on Britain's wealthiest to make an "extra contribution" to the economic recovery, in what has been widely interpreted as an attempt to win over restless Lib Dem activists ahead of the party's conference next month.
In an interview with the Guardian, the deputy prime minister suggested people of "very considerable personal wealth" could make a "time limited contribution" as the country faced a "longer economic war".
The Lib Dem leader is expected to flesh out his thoughts on a possible "wealth tax" at the party's autumn conference in Brighton next month, according to the report.
Clegg told the newspaper: "If we are going to ask people for more sacrifices over a longer period of time, a longer period of belt tightening as a country, then we just have to make sure that people see it is being done as fairly and as progressively as possible.
"While I am proud of some of the things we have done as a government I actually think we need to really hard-wire fairness into what we do in the next phases of fiscal restraint. If we don't do that I don't think the process will be either socially or politically sustainable or acceptable."
His comments appear to indicate a renewed bid to better differentiate his party's economic approach within the Coalition with David Cameron's Conservatives.
Clegg added: "If we want to remain cohesive and prosperous as a society, people of very considerable personal wealth have got to make a bit of an extra contribution."
"In addition to our standing policy on things like the mansion tax is there a time limited contribution you can ask in some way or another from people of considerable wealth so they feel they are making a contribution to the national effort? What we are embarked on is in some senses a longer economic war rather than a short economic battle."
He said his party could begin "spreading our wings more."
The proposal is not official government policy and will be seen as some as an attempt to mollify nervous Lib Dem activists ahead of next month's party conference in Brighton.
Last month Lib Dem policy adviser and chair of the left-leaning Social Liberal Forum, David Hall-Matthews, said many in the party wanted to see their ministers publicly challenging the Tories.
"It's time to start declaring what they would do if they won the next election too," he told The Huffington Post UK.
"Sure, they may also be shot down by the right-wing press - but at least their ideas will be out there for the public to judge. So let's hear Vince Cable's plans for full-blown wealth taxes, to finance the next rise in the income tax threshold."
Tory MP Bernard Jenkin dismissed the proposal as "pre-conference easy clap line."
"If the politics of envy made a country rich, we would be a very rich country," he told BBC Radio 4's Today programme.
"I think most rich people are contributing far more in tax than other people.
"I know this is not a fashionable view, but if you go on raising tax on rich people - and that's why, in agreement with Nick Clegg we have had to cut the top rate of tax from 50p to 45p - you drive wealth abroad.
Labour has reacted with scorn to the plan, with Chris Leslie, Labour's shadow treasury minister, saying Clegg was "taking the British people for fools".
"He talks about a tax on the wealthiest, but he voted for the tax cut for millionaires in George Osborne's Budget," he said.
"And he has supported a failing economic plan which has pushed Britain into a double-dip recession and is leading to borrowing going up by a quarter so far this year."