Nigel Farage said Ukip was "on the march" at the party's spring conference in Devon.
He told delegates it was "not inconceivable" the party could get MPs elected at the General Election in 2015, telling them: "this is our moment."
Ukip was the "biggest threat to the political establishment seen in modern times", Farage said, accusing the three main parties of "selling out British people" on immigration and Europe.
He set out Ukip's stall for upcoming local and Euro elections by saying Britain's relationship with the European Union would be the main battle ground.
On the topic of immigration from the EU, Farage claimed: "This country has frankly become unrecognisable. In many parts of England you don't hear English spoken. This is not the kind of country we want to leave to our children and grandchildren."
Labour and the Coalition government have failed the British people, he claimed. "The three so-called main parties did not lift a finger to stop immigration from Bulgaria and Romania in January," he said.
The conference in Devon was the first keynote event for Ukip since Farage admitted the party had a problem with "extremists" back in in January.
Farage claimed progress had been made in making Ukip more representative following outbursts blaming recent floods on gay marriage, and the recent antics of Godfrey Bloom - whom Farage blamed for ruining last year's summer conference. Bloom was reportedly absent from Torquay.
Farage claimed women candidates were well represented on candidate lists, stating that it was more likely the next Ukip leader will be a woman than in any of the other parties.
He laid into the Environment agency for the slow response to widespread floods which recently hit the south west and called for Britain's foreign aid budget to be diverted towards helping waterlogged householders.
Ukip had altered the public debate in Britain on issues such as immigration, he claimed.
Farage said: "We as a party have claimed back the idea that debating the European issue is not some appalling thing to do. We made the European debate respectable in this country.
"We've proved the point that it's not extremist to talk about immigration. It's responsible and the right thing to do. Our ruling classes have lost confidence in this country and that's why they've sold us out. They've cost us money and self-confidence."