The Prime Minister has said he is prepared to press the red button if he has to, as he looked to exploit Labour’s division on the nation’s security.
And he said that Labour leader Jeremy Corbyn’s recent comment that he would not authorise the use of nuclear weapons even if Britain was under nuclear attack “undermined national security”.
Mr Cameron said: “The problem with his answer is, if you … believe like me that Britain should keep the ultimate insurance policy of an independent nuclear deterrent, you have to accept there are circumstances in which its use would be justified.
“If you give any other answer then you are, frankly, undermining our national security, undermining our deterrent, ” he told BBC1’s Andrew Marr Show.
Mr Corbyn’s remarks in an interview marred the last day of the Labour Party Conference.
The party is significantly divided on the issue with a number of prominent Shadow Cabinet members seeking to retain the Trident system – which is up for renewal next year – and Mr Corbyn suggesting he was happy to accept a split on the issue.
Security is one of the three key themes of the Conservative conference – the others are stability and opportunity – and Mr Cameron will be seeking to capitalise on Labour’s division on the country’s defence capabilities.
Mr Cameron also confirmed there would be a vote on British military action in Syria – despite Russia’s recent intervention.
In a separate newspaper interview, he disclosed he would “beef up” the SAS and the number of drones Britain has to tackle Islamic State.
Mr Cameron told The Sunday Telegraph, the Ministry of Defence would buy a fleet of 20 Protector drones from the US. He said: “One of the biggest threats we have to respond to is the terrorist threat and that means a lot of things in terms of obviously domestic security and our intelligence services.
“But it also means making sure that we have the military equipment and resources we need – so seeing an enhancement of our Special Forces and particularly on the issue of surveillance aircraft.”
On Saturday, Mr Cameron said Russian strikes in Syria were hitting citizens and helping the “butcher Bashar al Assad”.
He said that few of the strikes were hitting IS targets. Defence Secretary Michael Fallon has said only one in 20 attacks have hit the terrorists.
The Prime Minister urged Russian president Vladimir Putin to work with Europe and the US to fight IS and not to prop up the Assad regime.
Mr Fallon and Foreign Secretary Philip Hammond will both speak at the conference on Sunday.
:: On tax credit cuts:
Mr Cameron ruled out any watering down of the tax credit cuts, which will see three million people lose £1,500 a year just before Christmas.
Asked if he would consider a review of the changes announced by Mr Osborne in the Budget, the Prime Minister replied firmly: “No. We think the changes we have put forward are right and they come with higher pay and lower taxes.”
He said: “We have had the vote in Parliament on tax credits and I think people respect this argument that the national living wage – a 50p increase next year, so a £20-a-week pay rise, rising to £9 by the end of this Parliament – that is a very significant change that really helps to make work pay rather than a tax credit system that recycles money back to people.
“Obviously I accept we are making changes to tax credits. We are protecting the lowest-paid people with child tax credits and what goes with it but we are moving to an economy where you get paid more and where you pay less in tax, rather than paying more in tax and getting the money back in tax credits. That is a better system.”
The Institute for Fiscal Studies has warned that it was “arithmetically impossible” for no one to be left out of pocket but Mr Cameron claimed their calculations were not right.
There had been some suggestion the Chancellor could announce a partial reversal of the cuts after increasing pressure and campaigning and claims they could be an “unexploded bomb” for his party leadership hopes.
:: On the EU:
The Prime Minister suggested he would be prepared to lead a Brexit campaign if he did not secure the EU reforms he is demanding from European leaders.
He said: “If I can’t get the things that Britain needs then I don’t rule anything out in the role that I would play.
Mr Cameron accepted that he could never satisfy the party eurosceptics no matter what deal was secured.
:: Lurch to the Right:
The Prime Minister said the Conservatives would remain firmly in the “common ground” and said that the party would not engage in any “back-slapping” this week on the fortunes of Labour.
He said: “As others are losing their heads and lurching off, we will be absolutely in the common ground, delivering for the working people of Britain.”
And he added: “There’ll be no complacency or back-slapping here this week – maybe a little bit of mild celebration of the election. The main theme is going to be about delivering people the things that we promised.”
:: On the NHS:
Mr Cameron announced a new GP’s contract that would free family doctors from box-ticking and put the focus on providing a seven-day NHS.
Speaking about junior doctors, he said: “We are going to have to make some difficult decisions” but said that parents want to have a service where they can see doctors when they needed.
He said: “A seven-day NHS is not just about GPs. It’s also about our hospitals. The fact is there are around 11,000 excess deaths because we don’t work properly at the weekend.
:: On the leadership contest:
The Prime Minister confirmed he would only serve two terms and said he thought “10 years is enough” but he said he was “passsionate” about having the top job and said: “I leap out of bed every morning”.
He denied suggestions that the way was being paved for Mr Osborne to take over and said: “It’s not a coronation because it’s not my decision.”
It has been suggested Mr Cameron will go in Spring 2019 to allow the new leader time to bed in before the 2020 General Election.
He said: “Now the effect it has on the Conservative Party – frankly, I would say it’s good we have a team, a team with stars in it and of course we will look at some of those stars and whether he or she would be able to do this job.
“Good. Frankly, great. People are asking ‘look at this person, look at that person’ – I want to run a team and that’s great.”
The Sunday Times today suggested there were as many as 18 ministers and former ministers prepared to take on the Chancellor, who in a separate interview said he would “see how it flies” when Mr Cameron steps down.
:: On that book
Speaking about the unauthorised biography, which contained some seamy allegations, Mr Cameron said the purpose of the book, as a form of revenge, was clear.
He said: “It think everyone can see why this book was written. I think everyone can see through it.” The book, Call Me Dave, is on sale on one of the party conference stands.