Rishi Sunak has said the next five years will be "some of the most dangerous yet" - but refused to set a date for a general election.
The prime minister said voters would face a choice between "the future and the past" at the general election and insisted he was "confident" the Tories could defeat Labour.
"It is only us, it is only me, that has the bold ideas and the clear plan that will deliver a secure future for the country," he told Sky News following a speech in London.
But he refused to say when he would call an election for, instead saying it would be "at some point in the second half of this year".
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In a wide-ranging speech that appeared to be a soft launch of his election campaign, Mr Sunak sought to position himself as the best option to navigate a dangerous period, adding that the war in Ukraine "has taken us closer to a dangerous nuclear escalation than at any point since the Cuban missile crisis".
The PM claimed Sir Keir Starmer could not keep the country safe because he once supported Jeremy Corbyn to be Labour leader and Sir Keir had not committed to increasing defence spending to 2.5% of GDP.
Mr Sunak said he remained "confident" his party could win the general election despite polls continuing to suggest the Tories are on course to lose.
He admitted "we haven't got everything right" over the past 14 years his party has been in power but said Labour "have almost nothing to say" about what they would do on most issues.
"No plans for our border, no plans for our energy security, no plans for our economy either," he said.
Mr Sunak said Sir Keir had "no principles either" and had gone from "embracing Jeremy Corbyn to Natalie Elphicke" - the Tory MP who defected to Labour - "all in the cynical pursuit of power. At any price".
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Tap hereHe claimed Labour "have no ideas" and act "like a pressure group, not of would be government".
Asked if he believed the country would be less safe under a Starmer leadership, and if this was the beginning of an argument that says "be careful what you wish for. Better the devil you know", Mr Sunak replied: "In a word, yes."
The PM said he could be relied on to make difficult decisions on the economy and defence, and he would make the UK a world leader in AI and technological advances.
Focusing on defence and technology, he said: "I feel a profound sense of urgency because more will change in the next five years than in the last 30.
"I'm convinced that the next few years will be some of the most dangerous yet the most transformational that our country has ever known."
Mr Sunak said the UK needs to be "prepared strategically, economically, with robust plans and greater national resilience".
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Labour frontbencher Jonathan Ashworth said Mr Sunak's speech - which Downing Street had billed as a "major speech" - was his "seventh reset in 18 months" and "just another desperate attempt to hide from the appalling record of this failed Tory government".
He said: "After 14 years of leaving the country less secure at home and abroad, the Tories have forfeited the right to talk about security.
"Millions of people are paying more on their mortgages, crime is going unsolved, dangerous prisoners are being let out early, the armed forces have been hollowed out and the NHS is on its knees.
"That is this government's record and the only way to turn the page and end the chaos is with a Labour government."
Liberal Democrat leader Sir Ed Davey said Mr Sunak should call a general election.
He said: "Families are sick of the Conservatives failing our NHS, allowing water companies to pump their sewage into our rivers and refusing to help families through the cost of living crisis.
"This Conservative government is out of touch and out of time and Rishi Sunak must do the right thing and give the people a general election."
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