Nigel Farage accused the British election watchdog of being "concerted" with Gordon Brown to raise doubts about his party's funding system, Brexit.
The prominent advocate of the holiday campaign said that he thought "a lot of people have worked together on this" in an exclusive interview with Sky News.
He attacked the Electoral Commission for visit the headquarters of his party two days before the European elections to study his system of payment of new supporters.
Former Prime Minister Brown used a speech on Monday to accuse Mr. Farage's new group of receiving a large sum of money via small "undeclared and untraceable payments".
He said that "under-the-counter payments" could be made and that people could pay to join the Brexit party in many currencies, including the Russian ruble.
A few hours later, the Electoral Commission announced that it would go to the party office the next day to "review the systems in place to receive funds."
A spokesman said his decision "was not related to the words of the former prime minister".
But Mr Farage said at a meeting the week before that the Electoral Commission had told him "that they liked our procedures" but that a request for formatting comments does not make any sense. has never been satisfied.
He told Sky News that they had decided to travel again as part of a "coordinated action" with Mr. Brown.
As an attacker at the independent body of the group overseeing the elections and political financing, he accused them of being "any political investment".
Asked to provide evidence to support his claim, it is made up of leftovers, Mr. Farage said: "Here we have a system of favoritism within politics.
"People go to the House of Lords, they go to the electoral commission.
"They come from the two and a half parties existing and the whole system needs to be changed."
A spokesman for the commission said the group had discussed party rules and systems at Brexit since it was registered.
"But recently, the public was worried about how the party raised its funds," they said.
"We have not seen any evidence of electoral infractions, but the law in this area is complex and we want to make sure the party systems are robust."
"We are an independent and impartial organization reporting to Parliament.
"We regulate what is proportionate to the issue, regardless of the politics of a party."
A new group of MEPs is expected to be elected on Thursday, due to Parliament's refusal to reach an agreement on Brexit.
Prime Minister Theresa May has made three attempts to sign a withdrawal agreement and is preparing a fourth. She announced her last shot in early June.