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UKIP leader Nigel Farage has urged people to "vote with your heart" and support the party on Thursday.
In a two-page advert in the Daily Telegraph, he said no party would win an outright majority, which presented an "opportunity to vote for change".
Mr Farage said UKIP offered "strong voices" that would "stand up to the political establishment".
But former Conservative leader Iain Duncan Smith said a vote for UKIP would be like a "suicide note".
He said it would destroy eurosceptics' hopes of a referendum on Britain's membership of the European Union by allowing a Labour government in to power.
Tory leader David Cameron has promised an in/out referendum on the EU if he remains as prime minister.
But Mr Farage has said, without UKIP holding the PM's "feet to the fire", he feared any referendum would not be "fair".
UKIP's double-page spread in the Daily Telegraph came as the party launched its final pitch to voters ahead of polling day.
Mr Farage warned voters against supporting either Mr Cameron or Labour leader Ed Miliband, accusing them of making broken and "empty" and promises and "appeasement of the SNP".
Only UKIP, a party which "transcends class and ethnic divides", could represent the whole of the British public and "stand up to the political establishment, be they in Westminster, Brussels, or indeed Holyrood".
With the UKIP leader: Robin Brant, BBC political correspondent
Is there a threat from IS on the streets of Sandwich? This was the question put to a man who stopped to talk to Nigel Farage in the Kent town today. He'd told the UKIP leader about his fears of "Arabs" and extremists coming to the UK.
It was the second time in as many days that a supporter had raised the issue off the cuff. Mr Farage spoke last week about what he sees as the dangers posed by Islamist extremists using the cover of migrants trying to cross the Mediterranean to get to Europe and the UK.
Today he said he can't believe the issue isn't bigger in this campaign. The man in Sandwich conceded that he felt no direct threat in his town [during a brief exchange I pointed out that the 7/7 bombers were British].
But Nigel Farage believes the fears of people - UKIP supporters - in Margate and Sandwich are genuine and it's something he's focusing on as polling day nears.