A Tory party spokesman was forced to deny Banks’ claims that his membership, and that of his spin doctor Andy Wigmore, had been approved.
Wigmore tweeted an image of what appeared to be a welcome letter from the party, but the Conservatives said such emails were often automated, and were sent before an application was finally accepted.
A party spokesman said on Thursday: “Arron Banks and Andrew Wigmore’s applications for membership of the Conservative Party have not been approved.”
Earlier, Banks said he was joining the Tories because he believed a leadership battle was coming. “We believe that the battle for Brexit is now within the Conservative party,” he told the Westmonster website, which he founded.
Brexiteers Banks and Wigmore were instrumental in the EU referendum campaign in 2016 and have said, in an article for the Westmonster website, that the battle for Brexit “is now within the Conservative Party”.
Banks said: “We believe that the battle for Brexit is now within the Conservative Party and the upcoming leadership election.
“Over 1.4m people follow Leave.EU online and we have urged them to join up and have their say.
“Most of our members are proper conservatives that believe in immigration control, family values, self reliance and prudent management of the economy.
“My Conservative Party membership lapsed in 2013 and I today joined the party.”
Banks taunted Tory Remainers Anna Soubry and Nicky Morgan on social media about his alleged entry into the party on Thursday.
The move comes following warnings earlier in the week of a risk of entryism in the Conservative party, after Leave.EU encouraged supporters to join to vote for a “true Brexiteer” to be the next leader if Theresa May was ousted over her Chequers Brexit plan.
On Wednesday, a Tory MP called for a change in the Conservative Party leadership election rules to make it more likely a pro-Brexit candidate succeeds May.
Writing in the Daily Telegraph newspaper, Andrea Jenkyns, MP for Morley and Outwood, said: “So we should be considering reforming the rules to allow for a members’ choice on the ballot, or a third ‘people’s’ candidate to join the two put forward by the parliamentary party.
“No more betrayal of our supporters,” she added.
Jenkyns is a vocal critic of the prime minister’s Brexit plan and praised Boris Johnson for quitting as foreign secretary over it.
Currently only two leadership candidates chosen by MPs go to a final vote of the membership. The system is seen as making it harder for candidates popular with party members to make it onto the ballot.