Nick Clegg promised a tax cut worth £700 a year to millions of taxpayers as he launched a Liberal Democrat agenda he said would "hardwire fairness" into British society.
The Lib Dems were the last of the three main parties to launch their manifesto for the May 6 General Election, on the eve of the first of the leadership debates which will pit Mr Clegg against Gordon Brown and David Cameron in a potentially decisive live TV face-off.
Both the Labour and Conservative leaders made pitches for the backing of Lib Dem supporters, as increasingly tight opinion polls suggested a hung Parliament may leave the third party in the position of kingmakers.
But Mr Clegg declined to say which party he would offer his support to in a "balanced" House of Commons, declaring instead: "I want to be Prime Minister."
The Lib Dem manifesto promised to change income tax thresholds to make the first £10,000 tax-free, funded by a crackdown on tax avoidance, the scrapping of tax breaks on pensions and capital gains which favour the wealthy and new levies on aviation.
Putting "fairness" at the centre of their agenda, the Lib Dems also pledged to cut class sizes in schools; introduce a £2 billion banking levy to pay for the bailout; lower the voting age to 16; and set a course for 100% of electricity generation from renewable sources by 2050.