British Prime Minister David Cameron delivers a speech on Fridayfrom the Velodrome in the 2012 Olympic Park to campaign for a “no” vote in Scotland's independence referendum later this year. (Oli Scarff/Getty Images)

British Prime Minister David Cameron waded forcefully into the debate over Scottish independence Friday, delivering an impassioned call to keep the United Kingdom together just seven months before Scots vote on whether to break up the three-century-old union.

On political, economic and military grounds, Cameron argued, Scotland is better off as a part of Great Britain. But Cameron also made an unusually emotional appeal, invoking Scotch whisky, the Sherlock Holmes franchise and the Team GB Olympics squad as examples of successful collaborations that would be diminished by a split.

“This is our home — and I could not bear to see that home torn apart,” Cameron said. “I love this country. I love the United Kingdom and all it stands for. And I will fight with all I have to keep us together.”

Polls suggest that most Scots agree that they should stick with their southern neighbors, and that Scotland will opt to remain a part of Great Britain in the Sept. 18 vote. But opinions remain fluid, and some surveys show those favoring independence gaining ground as the debate heats up.

Friday’s speech was politically treacherous for the prime minister. Cameron, and the Conservative Party he leads, are not popular in Scotland, which tilts left politically. He badly needs to keep the United Kingdom from coming unglued under his watch, but he also risks alienating Scottish voters if he becomes the face of those campaigning for a “no” vote on independence. His intervention could be perceived as just the sort of English imperiousness that the Scots are seeking to escape.

“It’s a tightrope,” said Nicola McEwen, who teaches politics at the University of Edinburgh. “If it becomes the British government versus the Scottish government, that plays into the hands of the independence movement.”

The leader of the Scottish independence drive, Alex Salmond, has repeatedly challenged Cameron to a debate. On Friday, after Cameron spoke, he renewed that push. “Let’s have that debate, instead of having a sermon from Mount Olympus,” Salmond told the BBC.

Other Scottish independence leaders accused Cameron of cowardice for giving the speech at the Olympic Park in London, rather than in Scotland.

Cameron has insisted that the choice in September is one the Scots must make themselves, and that they should be the primary players in any debate.

He acknowledged in Friday’s speech that “some people have even advised me to stay out of this issue — and not to get too sentimental about the U.K.”

But, Cameron said, “I care far too much to stay out of it. This is personal.”

McEwen said Cameron may have felt pressure to speak out because the “Better Together” campaign, as the anti-independence side is known, has struggled to come up with a champion who can match the rhetorical skills of Salmond. The 59-year-old leader of the Scottish National Party called the referendum after 2011 elections bolstered his control of the Scottish parliament.

That Edinburgh-based body wields power over matters particular to Scotland but yields to the British parliament on broader concerns such as security and economic policy. Independence would change that — though many of the particulars as to how the breakup would play out remain unknown.

By population, Scotland is only a small part of a union that also includes Wales, Northern Ireland and England — just 5 million people out of a total population of 63 million. But economically, militarily and culturally, it plays an outsize role.

Cameron on Friday directed much of his speech to those in the United Kingdom who live outside of Scotland, encouraging them to make their Scottish neighbors feel welcome and arguing that “we would be deeply diminished without Scotland.”

He cited the virtues of North Sea oil, Scottish shipyards and the hit television show “Sherlock” — which, as Cameron pointed out, was “written by a Scot a hundred years ago, played by an Englishman today — and created for TV by a Scotsman.”

The prime minister also trumpeted his skills as a pitchman for Scotch spirits, noting that “whether I’m in India or China, there’s barely a meeting where I don’t bang the drum for whisky abroad.”

Salmond, Cameron noted, is no less a salesman. But “the clout we have as a United Kingdom gives us a much better chance of getting around the right tables, bashing down trade barriers, getting deals signed.”