Prime Minister David Cameron has told a gathering of Conservative Party members in Stirling that "our Union" protects jobs in Scotland.
Members of the Scottish Tories are holding their two-day annual conference.
UK leader Mr Cameron began by saying there were "huge battles coming".
He said 2014 was about saving the UK; 2015 was about giving Britain the Tory government it needed and 2016 was about giving Scotland "strong alternatives".
Voters in Scotland will go to the polls on 18 September next year to take part in a referendum on independence.
They will be asked the yes/no question: "Should Scotland be an independent country?"
The Scottish Conservative Party, led by Ruth Davidson, is the last of the four main parties to hold a 2013 conference.
Mr Cameron was the keynote speaker on the first day. He told delegates that in Ms Davidson they had the "ideal leader".
He said: "Ruth wasn't born into the Conservative Party - she chose it. And she understands that to win we've got to be a party for all of Scotland."
A deal setting out terms for a Scottish independence referendum was signed by Mr Cameron and First Minister Alex Salmond in October last year.
The agreement, struck in Edinburgh, has paved the way for a vote which will also allow 16 and 17-year-olds to take part.
During the address Mr Cameron questioned the SNP's plans for keeping the pound in the event of Scottish independence, saying that a shared currency could only work with political union.
He added: "We said we're better together as one economy with a shared currency.
"Alex Salmond said no - let's go our separate ways but let's still keep the pound.
"How would that work? Has Alex Salmond not seen what's happened in Europe over the past two years? You can't make a currency union work without a political union.
"We said we're better together to protect jobs in Scotland's great defence industry. Alex Salmond said no - we're scaremongering. "
Mr Cameron continued: "But what's the evidence? There are 12,000 people across Scotland employed by defence companies - backed by a British defence budget that is the fourth largest in the world.
"Make no mistake - our Union protects jobs. "
The speech did not just focus on the future of the UK.
The prime minister also spoke about tackling the deficit, encouraging enterprise and cutting the country's welfare bill.
Mr Cameron said one of the biggest challenges was "sorting out welfare".
He argued: "Our welfare system has become unaffordable: last year we spent £24bn on housing benefit alone. That is a lot more than we spent on doctors' salaries in our NHS.
"It has become unsustainable - one in every £7 we spend is on working age benefits. Not pensions - benefits for people of working age.
"It's become unfair - for years now, the income of those on benefits has risen faster than wages.
"And so that's why we're rolling out a benefits cap - so a family on benefits can't earn more than the average family in work."
Mr Cameron said dealing with "our debts" was not an "optional extra - it was an absolute necessity".
He added: "We all know the risks we take if we keep on running a massive deficit.
"You can't borrow your way out of a debt crisis.
"You know how much we spent just on servicing Labour's debt last year? Forty-seven billion pounds.
"That's equivalent to the entire NHS budget in Scotland for the next five years. That can't go on."