Analysis By Nick Assinder Political correspondent, BBC News website

The Liberal Democrats must occasionally feel they are just a think tank for the bigger political parties.

The Lib Dems say the new proposals will be "tax neutral"

One of the regular complaints from the party's leaders is that their most carefully thought through and eye-catching policies have been stolen almost before the ink has dried on them.

Nowhere have they claimed plagiarism more than on taxation. A 1p rise in the basic rate to fund education spending, green taxes and abolition of the 10p rate have all been pinched in one form or another.

So, once again, Sir Menzies Campbell's team have had to come up with something to give them a unique selling point.

And this year's unique selling point is to cut the basic rate of income tax by a massive 4%, with the bill being met by increased green taxes and a squeeze on the "very rich" top 10%.

So, will the other parties be as eager as ever to steal bits of this policy?

Very wealthy

One problem may be that the idea of taxing the top 10% has a very Old Labour ring to it - the sort of "squeeze the rich" policy once so loved of Labour chancellors.

That might not worry some of the more left-wing grassroots Lib Dem party members, but it will come as a great surprise if it delights the newer, free-market thinkers in the party.

Mr Cable says he will tax the wealthy

Then there is the point at which the party believes a family becomes "very wealthy".

According to the policy's architect, treasury spokesman Vince Cable, that is when they have joint income of around �68,000 a year, not exactly the David Beckham league.

He has admitted that would mean some 2 million people losing out - around 10%.

"The corollary of that is that 90% would be better off. The vast majority of people on low and middle incomes would be significantly better off because most of the increased taxation would come from the very wealthy," he said.

Added to that, the policy of abolishing the council tax in favour of a local income tax would also benefit those, such as pensioners, who have a low income but whose home has appreciated in value.

Find favour

Those pensioners are of course part of the age group most likely to vote at an election, so taken together with the 90% of households due to be better off, the Lib Dems might well believe they have put a vote-winning tax plan together.

The other side of the argument is that it may well be that voters are no longer wowed by headline-grabbing cuts in the basic rate since Mr Brown's final Budget.

He went for that approach only to see the policy quickly under attack after it emerged he had compensated for it by abolishing that lower 10p rate, so bringing more of the poorest into a higher 20p band.

Still, what the Lib Dem policy offers is a genuine shift in the basis of taxation which will create many more winners than losers.

The party is certainly not attempting to disguise the shift, instead making a virtue of the "hit the rich" proposals.

In doing so they are seeking to punch right and left - appealing to old Labour sensibilities and also to the aspirational Tory voter longing to see the promise of a clear cut in their tax bills.

The test of that may not just be in the ballot box at the next election, however.

It may be to what extent the other parties decide to cannibalise the package.