The Liberal Democrats would tax the rich to cut workers' national insurance payments "immediately" after reaching their long-term aim to take millions out of income tax.

Party leader Nick Clegg will today signal he wants to continue putting money back into the pockets of ordinary people if he is in the Government after next year's General Election.

But with the LibDems struggling in the polls, he also hinted at a life after politics, saying he was not a "Duracell bunny" and would not "go on forever".

The party has been forced to respond after Prime Minister David Cameron's pledge last week to also raise the income tax threshold, to the LibDems' long term target of £12,500.

Mr Clegg accused the Tories of "plagiarising" LibDems policy, but said the party had failed to explain how they would pay for it.

By contrast, he said, the LibDems would fund the move with an increase in capital gains tax on the wealthy - hitting share income and second homes.

Mr Clegg will also round on Mr Cameron over his plans to restrict Scottish MPs voting rights in the House of Commons.

The Prime Minister made his shock announcement on September 19, just hours after the results of the Scottish independence referendum.

Mr Clegg will accuse Mr Cameron of being "at it" and trying to impose an "entirely self-serving system of Tory votes for English laws ... in order to give more say to their MPs".

Today an emergency motion at conference will call on the Prime Minister to implement the vow on extra powers for Scotland in full "without any conditionality".

Mr Clegg accused the Tories of planning to "penalise the working-age poor" with welfare cuts. The LibDem leader said his message to voters was: "We have cut your taxes in this Parliament and we will continue doing just that in the next.

"It is easy to promise a tax cut, it is much more difficult, especially in the current economic situation, to say who pays.

"This is about priorities. The Conservatives may have copied our flagship policy but they would pay for it in a deeply unfair way - by hitting the working poor.

"And the Conservatives want to cut taxes for the better-off by nearly five times as much."

Aides to Mr Clegg suggested the rate of capital gains tax could be raised from 28 per cent to between 35 and 40 per cent.

Mr Clegg will set out plans to raise the personal tax threshold to £11,000 in the first year of the next Parliament. He will not commit to a timetable to push the figure to £12,500.

But once that target had been reached, the party's tax priority over the long term would be to increase National Insurance thresholds to the same level as those on income tax, he will say.

In a round of broadcast interviews at the conference in Glasgow, Mr Clegg also said the choice of either Labour, whose leader Ed Miliband famously forgot to mention the budget deficit in his conference speech, and the welfare-cutting Conservatives was an "unappetising" one for voters.

He accused internal party critic Jeremy Browne of "talking out of the back of his head" when he said the conference slogan 'Stronger Economy, Fairer Society' implied the LibDems could only hope to mitigate the excesses of other parties rather than pursue their own vision.

But with recent surveys putting the LibDems on about 7 per cent in the polls, Mr Clegg also appeared to hint at a life after politics.

He insisted he would not "go on forever" as Liberal Democrat leader - after Energy Secretary Ed Davey admitted voters had "fallen out of love" with the Deputy Prime Minister.

Saying he did not think a "great deal" about life after politics, Mr Clegg added: "I'm 47, I've got three little kids, I've got lots of interests outside politics and lots of friends outside politics. I'm frankly too busy to do that. You should be dedicated to your job but not obsessive about it."