By Ross Hawkins
Political correspondent, BBC News
UKIP faces competition from new Eurosceptic parties
The leader of UKIP Nigel Farage thinks he can beat Labour into fourth place at the European elections.
At the launch of his party's Euro campaign he said the humiliation could bring down the prime minister.
Some in Westminster and Brussels will scoff at that, but UKIP has form.
At the last European elections in 2004 it won 12 seats in the European Parliament.
Overnight the former TV presenter - Robert Kilroy-Silk - became Britain's best-known MEP.
Then, as now, the party's suggestion was a simple one - Britain should withdraw from the European Union.
It said that would save the country money and give the government more control of immigration.
Since its election triumph, life has been difficult for UKIP.
One of its MEPs, Ashley Mote, was convicted of benefit fraud.
Another - Tom Wise - was charged with false accounting and money laundering. He has denied the charges.
Neither now sits as a UKIP MEP.
Robert Kilroy-Silk has long since walked away from the party, having failed to become its leader.
At the launch of UKIP's European campaign Nigel Farage said the party had a policy of not employing any more daytime television stars.
Like many political leaders who struggle for attention outside election times, he thinks this campaign could give him all the publicity he needs without Kilroy's celebrity firepower.
He said: "If we have this national debate, if we are able to discuss European issues and their impact on people's lives, then I think we will have another big surge towards UKIP over the course of the next month."
Nigel Farage's political future depends on that surge. He told a magazine he would resign if UKIP won fewer than 10 seats in the European Parliament.
It will not be easy to meet his target. Voters with doubts about the EU may turn to the Conservatives or one of the other smaller parties concerned about Britain's position in Europe.
Next month's elections will show whether UKIP still has potential to be a giant-killer, or whether it has been weakened by growing competition and difficult headlines.