The chairman of Reform UK has predicted the party could win “350 to 400 Members of Parliament” at the next general election.
Zia Yusuf also told the BBC he does “understand” any potential concerns over the prospect of the party accepting a donation from tech billionaire Elon Musk.
It comes after Reform topped a YouGov voter intention poll for the first time this week.
The party returned five MPs in July’s general election but came second in 98 constituencies.
Talking about the polling results on BBC Radio 4’s Political Thinking podcast, Mr Yusuf said he thought his party “will win between 350 to 400 Members of Parliament” at the next general election, which must be held before August 2029.
Reform UK came top in the YouGov poll with 25% support, compared with Labour on 24% and the Conservatives with 21%.
The polling company said the one-point lead is within the margin of error.
The party also recently topped a national opinion poll by Find Out Now, with 26% support.
Reform leader Nigel Farage met Tesla, X and SpaceX owner and Donald Trump ally Mr Musk in December, with the billionaire rumoured to be considering a large donation to the party.
Reform UK leader Nigel Farage speaking during the Reform UK North West Essex conference last month
Rules preventing foreign donations mean Mr Musk could only funnel any donation through one of his UK-based businesses.
Political parties can accept donations from a number of sources, including individuals on the UK electoral register or a UK-registered company.
Asked about concerns over donations from the tech billionaire, Mr Yusuf told the podcast: “I can understand those concerns… We’re going to play by the rules.”
He said the party is “not a pressure group” and is “here to win”.
“We need 350 to 400 incredible Reform MPs to transform the country,” he added.
Pushed on whether he would want Mr Musk’s money to make that happen, Mr Yusuf said: “Who knows if he will or he won’t, but if he was to make a donation and it was within the rules and it helped us win, then why not?”
The YouGov result was the latest in a series of polls which suggest Reform have pulled level with, and possibly overtaken the Conservatives in public opinion.
Mr Yusuf suggested on the podcast he would be open to former Tory home secretary Suella Braverman joining Reform.
He said he has a “huge amount of respect” for Ms Braverman, who is MP for Fareham and Waterlooville, and when asked if she would be a good Reform member, he responded: “If Suella wanted to join Reform UK? Yeah, absolutely.”