Robert Jenrick said that any MPs who want to follow his move to Reform UK have got to “make their minds up soon”.
The former shadow justice secretary, who was sacked by Tory leader Kemi Badenoch on Thursday hours before he announced his defection, said the party is “moving fast”.
Speaking ahead of a Reform UK rally in his constituency of Newark in Nottinghamshire, Mr Jenrick told LBC that MPs who share the party’s values are “welcome” to join.
Asked who he would like to see join the party, Mr Jenrick said: “Well, Nigel (Farage) has said that any member of parliament who shares our values and principles is welcome in Reform.
“But they’ve got to make up their minds soon, because this party is moving fast. And after the May elections, we really hope to have made massive progress across the whole of the country.”
During his speech to hundreds of Reform supporters, who welcomed him with cheers, Mr Jenrick said of his defection: “I have never felt stronger and more certain about anything I have done in my life.
“I was forced to resign and I rebelled against my own party to fight for something that would actually work.
“In joining Reform, I have resolved to never, ever defend the indefensible again.
“I didn’t just leave the Conservatives because they can’t fix Britain, and they can’t, take my word for it … I left because Reform will fix Britain.”
Tory MP Andrew Rosindell announced on Sunday evening that he was the second Conservative MP to join Reform in the space of a week, after Mr Jenrick.
Mr Rosindell, who had been a Conservative member since 2001, said he was persuaded to resign as a shadow foreign office minister in Kemi Badenoch’s front bench because of the “failure” of the Conservative Party “on the issue of Chagossian self-determination”.
Reform UK leader Nigel Farage said the centre-right of British politics is “coming together as one under the banner of Reform”.
He told his supporters at the rally: “We will replace the Conservative Party as the main opposition party in British politics.
“The next general election may be our last chance to turn this country round and we are determined, and, you know what, we are going to win.”
Asked in an interview with the BBC before the rally if he was convinced he was not going to fall out with Mr Jenrick after a few days of working together, Mr Farage said: “So far, so good. There’s no reason why we should.”
He added: “He was odds-on favourite to be the next leader of the Conservative Party. He’s made this move because he believes in what we stand for.
“I think it was logical, perhaps inevitable, he was going to join us.”
Reform UK chairman David Bull said at the rally that the Tories can “never, ever be trusted again”.
He said: “Let me tell you, we have not seen the benefits of Brexit that we were promised, and that is down to poor planning and abysmal leadership.”
He added: “So, to recap, what did the Tories actually give us? They gave us open borders, a shattered economy and a broken healthcare system. Let me tell you, the Tories can never, ever be trusted again.”
He added that Reform was “utterly delighted” to welcome Mr Jenrick to the party, which now has seven MPs.
