David Cameron described negotiations to reform the UK's relationship with Brussels as "bloody hard work" as he refused to rule out recommending a British exit from the European Union.
As Tories gathered for a conference set to be dominated by Europe and the crisis in Syria, Mr Cameron said he was "calmly and rationally" attempting to persuade European counterparts to back his drive for reform ahead of an in/out referendum on the UK's EU membership.
Mr Cameron also announced new measures to combat the threat of Islamic State (IS), with extra drones on order and more funds for special forces.
In an indication that Mr Cameron will not push for an early vote on whether to sever ties with Brussels, the Prime Minister told the Sunday Telegraph there was "plenty of time" for European counterparts to consider his demands before the deadline of holding a public vote by the end of 2017.
"I'm confident I've got the right strategy, the right plans, the right team to deliver it," he said. "I've just got to get on with it ... it's bloody hard work."
The Prime Minister insisted that European leaders were aware of the stakes involved and that the UK would be prepared to vote to leave if he could not secure reforms.
"I think they know that this is a serious issue, a serious negotiation," he said.
"They know that this is an in-out referendum."
Mr Cameron said people should not think that his approach to the negotiations meant he was not making headway.
"Just because I haven't been doing it with a gun held to my head. I've calmly gone round every European capital.
"Because I've done it calmly and rationally, don't mistake that for a lack of real zeal in fixing what's wrong."
The Prime Minister again insisted he believed the UK should remain in a reformed EU, but stressed: "I've always said if we don't get those things that we are asking for I rule nothing out and I am very serious about that."
Mr Cameron hopes to put defence and security at the heart of the Tory conference agenda, highlighting the steps being taken to bolster the military's ability to tackle IS.
The RAF's fleet of Reaper drones will be more than doubled, to over 20, and upgraded with the very latest technology in the new Protector designation.
The aircraft will dramatically increase the UK's ability to identify, track, deter and ultimately counter potential threats.
Special forces troops, including the SAS, will be equipped with new specialist weapons and clothing.
Mr Cameron indicated he believe it "may well become possible" to win a Commons vote in favour of extending the RAF's bombing campaign into Syria by relying on the votes of Labour MPs despite Labour leader Jeremy Corbyn's opposition.
The Prime Minister, who has said he will seek a Commons vote unless he is sure there is a "consensus" for action, said: "I think it's the right thing to do. I think it may well become possible but you know we will continue doing what we're doing until it does."
Asked whether there would be more missions in Syria targeting British jihadists, following the strike which killed Britons Reyaad Khan and Ruhul Amin, Mr Cameron said: "It's obviously a last resort. It's only the right thing to do if there are no other avenues you can take.
"What we try to do is stop people travelling to these regions, confiscate their passports, work with local government to have them arrested or detained. We try and take every step we can but at the end of the day we have to keep the British people safe from terrorist threats."
The focus on defence comes after the end of Labour's conference was overshadowed by a row over Mr Corbyn's support for unilateral nuclear disarmament.
Mr Cameron's arrival in Manchester for the first autumn conference of a majority Tory administration since 1996 came amid protests at the Government's continued austerity measures.
Outside the secure zone surrounding the Midland Hotel and Manchester Central conference centre, a handful of demonstrators staged a noisy protest.
Thousands of protesters are expected to take part in a march as the conference formally opens, while Mr Corbyn is expected to address a public meeting in Manchester on Monday.