The British prime minister David Cameron has said he is prepared to 'press the red button' if he has to, as he looked to exploit UK Labour's division on the nation's security.

He also disclosed he would "beef up" the SAS and the number of drones Britain has to tackle Islamic State.

Mr Cameron told The Sunday Telegraph that the UK's defence ministry would buy a fleet of 20 Protector drones from the US.

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. British defence secretary Michael Fallon has said only one in 20 attacks have hit the terrorists.

Mr Cameron urged Russia's president Vladimir Putin to work with Europe and the US to fight IS and not to prop up the Assad regime.

Mr Cameron also confirmed there would be a vote on British military action in Syria - despite Russia's recent intervention.

National security

On the first day of the Conservative Party Conference in Manchester, Mr Cameron said in a televised interview he believed the country should retain the Trident nuclear deterrent.

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 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 Britain's defence capabilities.

The prime minister has also 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.

Speaking about the recent unauthorised biography of the prime minister, 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.

Protests

Meanwhile thousands of protesters will be marching through Manchester as the Conservative party conference gets underway in the city.

The anti-austerity campaigners - backed by unions - are demonstrating against the party's policies, including reforms to welfare.

Musician Billy Bragg, who is speaking at a pre-march rally, says Labour has found its voice again: