Ukip is the most successful political pressure group of the 21st century, the party's economic spokesman claimed on Monday 15 May.
Patrick O'Flynn MEP made the remarks to IBTimes UK after warning that Conservative Chancellor Philip Hammond was planning a "targeted" tax attack on Britain's self-employed.
"No one has ever measured the success of Ukip according to a chart of how many people we get in the House of Commons," he said.
"We are perhaps the political party that has been the most successful pressure group of the entire 21st century in terms of the EU agenda, in terms of the debate over immigration and over mass immigration."
O'Flynn, a former journalist, said he had decided to concentrate on Hammond because the general election was "unusual".
"It appears that it's a foregone conclusion Philip Hammond will be walking back into Number 11 Downing Street unless those rumours of the disagreement between him and the prime minister turn out to be even more severe than we think," he said.
O'Flynn added: "My challenge to Hammond is to prove in this election campaign via the economic policies that he sets out that the Tories are not mainly in it for the rich. Despite his party's poll rating, that is what millions of voters think."
Ukip want the Tories to explicitly rule out a National Insurance "raid" after Hammond was forced to U-turn over such a proposal in March. The 2015 Conservative General Election manifesto promised not to increase income tax, National Insurance or VAT.
So far Theresa May's party have failed to repeat David Cameron's "triple lock" tax pledge. Ukip, meanwhile, are struggling in the polls.
The latest YouGov survey, of more than 1,600 people between 11 and 12 May, put Ukip on just 3% (-2). The party won almost 13% of the vote at the 2015 General Election.