Clegg's statement of intent

What does Nick Clegg mean when he talks in the Guardian of a new "time-limited contribution" by the wealthy?

My understanding is that he does not - yet, at least - have a specific measure in mind.

This is a statement of intent, directed partly at reassuring his party, partly at signalling to the country and partly to the Conservatives, that he will not allow the next phase of austerity to focus on the poorest in the land.

The chancellor signalled in his last Budget that he would be looking to cut the welfare bill by a further £10bn to meet the cuts made necessary by his earlier announcement that austerity would continue for two more years from 2015.

His main challenge may not be George Osborne, though. I'm told that before the last Budget the chancellor was willing to trade a cut in the top rate of income tax to 40p - not 45p as was announced - in return for agreeing to a version of the Lib Dems' Mansion Tax.

It was David Cameron who vetoed both ideas.