Nigel Farage has accused Downing Street of being "petty" and "small minded" for allegedly banning him from meeting Donald Trump next week.
The Brexit Party leader said Number 10 had told the US president's team not to meet him during his state visit – a move he branded "absolutely ludicrous".
Mr Farage told the Press Association that a friend in Washington had informed him that Theresa May's office had told Mr Trump's entourage: "Don't meet this guy."
"It's absolutely ludicrous," Mr Farage said.
"I know they're worried about their Conservative Party but given that I've got good connections to him and many of the team around him and that they're our biggest military ally, intelligence ally, and very important investor in each other's countries – why would you want to prevent a meeting between someone who knows the president well?
"It's just extraordinary, it's small minded, petty and it's not putting the interests of the country first."
A Downing Street spokesman said: "Who the President meets during his visit is of course a matter for him."
Asked about Mr Trump's comments that Boris Johnson would be an "excellent" choice to replace Mrs May as Conservative Party leader, Mr Farage said: "He obviously likes Boris, and he obviously thinks Boris believes in Brexit.
"Trump is clearly a Brexiteer – he's never made any bones about that, so yeah he likes Boris. He quite likes Jeremy Hunt by the sounds of it too."
Mr Trump will be in the UK for a three-day visit from June 3-5, and earlier this week said Mr Farage was a "friend of mine" and a "good guy".