Nigel Farage, leader of the UK Independence party, has admitted on the eve of the European election campaign: "We're whistling in the wind if we think we can implement a Eurosceptic agenda from within the European parliament."

He also said "we cannot change a thing in Europe" and that while Eurosceptics could "have some fun" in the European parliament trying to block legislation, it would "not last very long".

Farage's remarks at a TaxPayers' Alliance event on 18 February emerged on the eve of Ukip's spring conference on Friday.

In his speech, Farage said he did not think it would be possible to secure a 33% blocking minority of MEPs across the parliament after the elections, even though he says "the important thing for Ukip is to lead the group that is bang in the middle of the sceptic movement in parliament".

He said: "Are we going to get 33% of MEPs? I don't think we are. I suspect between 20% and 25%."

The Eurosceptic MEPs from the political left and right, he said, might include "all sorts of people that you wouldn't want to take home to meet mum for tea on Sunday afternoon". But he stressed he would not form any alliances with fascist groups such as the French Front Nationale.

Farage's forecast that sceptics will not be able to achieve anything in the European parliament after the elections raises questions as to the purpose of electing Ukip MEPs to the parliament, especially in view of the party's erratic voting record in the previous parliament.

Tim Farron, the Liberal Democrat president, said: "Ukip MEPs don't turn up for key votes that affect British jobs, they don't work for their constituents and they don't stick up for Britain. More Ukip MEPs means fewer people working hard to protect Britain's interests in Europe. Our MEPs work hard all year round to protect British jobs."

Farage is due to speak to the party's spring conference on Friday. As many as 800 delegates are due to attend, underlining the extent to which Ukip has become a political phenomenon.

At the Taxpayers' Alliance meeting Farage predicted the far right would do well in the elections, saying Golden Dawn, the Greek neo-Nazi party, would certainly win seats in the European parliament. He also predicted the Front Nationale "will probably win the elections in France".

Farage is also adamant that his party is now a permanent force in UK politics. He added: "I genuinely think that Ukip has a serious chance of topping the national poll in those elections," he added.

He claims those elections may represent the most significant change in British politics for 100 years.

"I want us to use the European elections to cause an earthquake in British politics, to change the Labour party position on the European referendum, for the Conservative party post the European elections, well you guys will have to decide whether you think Cameron is the right person to lead in 2015 or not.

"And as far as the Liberal Democrats are concerned, well if you look at the numbers they're right on the edge, and they could face total wipeout on 22 May. It really couldn't happen to nicer people."

He also claims it is possible his party may hold the balance of power after the general election next year. "If we're able, sensibly and ruthlessly actually, as the Liberal Democrats did in the 1990s to target our resources on those seats that are winnable, and there may be some fellow helpers in those areas. My ambition would be that Ukip in the next Westminster parliament holds the balance of power, as the Lib Dems did in the last parliament of 2010."