The Electoral Commission has defended visiting The Brexit Party’s offices to review how the party receives funding.
Party leader Nigel Farage accused the watchdog of acting “in bad faith” and “interfering in the electoral process”.
But the watchdog said there had been “significant public concern” about the way the party raises funds.
A spokesperson said there was no evidence of electoral offences, but added: “We want to satisfy ourselves that the party’s systems are robust.”
On Monday, former Labour Prime Minister Gordon Brown attacked The Brexit Party for receiving a large amount of money via what he called “undeclared, untraceable payments”.
However, Mr Farage dismissed that attack as a “smear” and suggested there might be collusion between the Electoral Commission and Mr Brown.
“I’m certain of it – I’m certain the establishment are working together,” he told the BBC.
The commission said in response: “Our regulatory work during this campaign – for the European Parliamentary elections – has not deviated from our usual approach.
“Our decision to visit is not related to comments made by the former prime minister.”