Lee Anderson has been unveiled as the first-ever MP for Reform UK, with the former Conservative party vice-chair telling a press conference that he had joined the Nigel Farage-created party because: “I want my country back.”

During a sometimes chaotic event in Westminster, in which the Nottinghamshire MP was announced as a defector by Richard Tice, Reform UK’s leader, Anderson promised to help his new party “fight back in the culture war”.

Confirming the move, which he had declined to rule out last month, Anderson said he had not told any Tory colleagues in advance and had given prior notice only to his family – and a few hours before the event to GB News, which pays him £100,000 a year as a presenter.

Neither Tice nor Anderson would comment directly on speculation about other backbench Tories who might also sign up to Reform, but the Reform leader said he would be “surprised” if no one else followed suit before the election.

While one Conservative MP said it was possible that “one or two” colleagues might also defect, others were doubtful. “I doubt that he will be joined by others,” one former cabinet minister said. “Lee has his own agenda, which seems to be linked to a media career.”

Speaking to reporters after the press conference, Anderson said he would have defected even if Rishi Sunak had not stripped him of the Conservative whip last month over comments he made about Sadiq Khan, the London mayor, condemned as Islamophobic.

The MP said he had been convinced to make the move after his parents, who live in his Ashfield constituency, told him they would not be able to vote for him if he remained a Conservative.

He dismissed comments he made in January about Tice being “a pound-shop Nigel Farage” as banter and confessed to trying to throw journalists “off the scent” by pretending he had no interest in joining Reform.

He did admit to feeling “a little bit bruised” about leaving the Tory benches, saying he expected to now have to sit next to the new Rochdale MP, George Galloway, in the Commons.

“I’ve got a lot of [Conservative] friends that sit on the benches with me, who have shown me a hell of a lot of support,” he said. “So I’ll be sad to leave them, but if I’m honest, unfortunately a lot of my colleagues won’t be there in a year’s time.”

Asked if he would remain an MP after the election, Anderson insisted he would: “My mailbag tells me I’m going to win.”

Addressing the press conference, Anderson said several times that he wanted his country back, echoing the language about Khan, in which he said the London mayor, who is Muslim, had “given our capital city away to his mates”.

“My opinions are not controversial. They are opinions which are shared by millions of people up and down the country,” he said, citing subjects such as migration and the policing of pro-Palestine marches in London.

“It’s not controversial to fight back in the culture war, a culture war that is sweeping our nation.

“But now like millions of people in this country, I feel that we are slowly giving our country away. We are giving away our way of life. We are allowing people to erase our history. We are giving up our streets to a minority of people who literally hate our way of life. We are letting people into our country that will never integrate or adopt our British values.”

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The defection gives Reform UK, formed by Farage as the Brexit party in 2018 after he exited an imploding Ukip, its first-ever Westminster voice.

Ukip had two MPs in 2014, after defections, holding both seats in byelections. One of them, Douglas Carswell in Clacton, went on to retain his seat in the 2015 general election. Anderson, who had a 5,700 majority when he won his seat in 2019, intends to try to stay on as a Reform MP.

Anderson’s move, while widely expected, will spook the Conservatives, in part as it will increase the media focus on Reform, which is polling at up to about 13% but has struggled to break through under Tice.

An increase in support for Reform would further damage the Tories’ electoral hopes. While Tice has said he hopes to “obliterate” the Conservatives, Anderson said he did not share this wish, saying such differences were allowed in “the party of free thinking”.

Danny Kruger, a co-leader of the New Conservatives grouping of Tory MPs, which had counted Anderson as a member, said that Anderson’s move to Reform should come as a warning to Sunak’s party.

“It reflects the fact that as a party we have lost the coalition of voters who voted for us back in 2019,” he told Politics Live on BBC One.

“I think today is a wake-up call for us as a party to try to reassemble that coalition. We need to be much more deliberate about the policy platform that will win back those voters who left us.”.

James Cleverly, the home secretary, said he was disappointed at Anderson’s move. “I think he’s made a real mistake,” Cleverly told broadcasters at an anti-fraud summit. “As he has said, in his own words, Reform is not the answer, and a vote for Reform will only let in a Labour government.”

Anderson, who began his political life as a Labour councillor before defecting to the Conservatives, said he would not resign and call a byelection in his seat after switching parties again, arguing: “It would be pretty reckless of me to suggest a byelection when we could have a general election in May.”