Scotland has voted against independence, deciding to remain part of the United Kingdom. Now the process to devolve further powers to Scotland begins. WSJ's Mark Kelly reports.

At the Marriott Hotel on Glasgow's Argyle Street early Friday, well-dressed delegates from the pro-U.K. Better Together campaign's sipped American beer, snacked from an Indian buffet and cheered when turnout in the pro-independence bastion Dundee fell short of the numbers expected.

They knew Scotland was staying in the 307-year-old union at the heart of modern Britain.

High turnout was just one of the factors that propelled the pro-U.K. campaign to victory in Scotland's referendum on staying with England, Wales and Northern Ireland or going it alone as an independent country.

What had at one stage appeared to be a pedestrian campaign in comparison to its fleet-footed pro-independence rival found a new urgency in the final weeks ahead of the poll. Experts say that helped it hang on to its lead against a last-minute surge in separatist support.

Scottish voters awoke Friday to find their country will still be part of the United Kingdom after a historic referendum. WSJ's Jenny Gross reports from Edinburgh. Photo: AP

"We have chosen unity over division," said Alistair Darling, a former U.K. finance minister and leader of the Better Together campaign, early Friday when victory was assured.

Yet the final tally—55% of Scots who voted chose to stay in the U.K. and 45% cast their ballot for independence—was tighter than many had predicted.

Until a month ago, polls showed Better Together was consistently ahead in opinion polls. Officials in the pro-union "no" camp were energetically focusing their fire on what they saw as a misstep of the "yes" campaign: Its attempt to craft a one-size-fits-all message to draw disparate groups to its crusade.

"Yes" supporters included such unlikely bedfellows as Scottish communists and transport tycoon Brian Souter. Artists and writers rubbed shoulders with radical environmentalists and traditional Scottish nationalists.

Trying to satisfy all these groups and appeal to average Scots meant the case for independence put forward by Scottish National Party leader Alex Salmond was full of holes, said Alistair Carmichael, secretary of state for Scotland in Prime Minister David Cameron's governing coalition.

"Their strategy essentially invited a whole series of questions," Mr. Carmichael said—on currency, jobs and Scotland's place in the wider world—that the "no" campaign exploited.

Scottish First Minister Alex Salmond on Friday in Edinburgh. Getty Images

Currency was a potent and favorite line of attack, as Mr. Salmond's insistence on keeping the pound in the teeth of London's opposition underpinned his economic pitch to voters.

Still, the "no" camp's strategy appeared to be misfiring. A poll by YouGov in early September that put "yes" ahead for the first time stunned the U.K. Parliament and electrified the referendum campaign.

Officials say that after a Sept. 8 meeting on security issues, Mr. Cameron and opposition leader Ed Miliband, whose Labour Party faced electoral catastrophe if Scotland seceded, hastily cleared their schedules and headed to Scotland that week with Nick Clegg, leader of the Liberal Democrats, Mr. Cameron's coalition partner.

In an attempt to preserve the union from an independence juggernaut, the three leaders agreed to a pledge to give the Scottish parliament more power. But as they raced north, they were upstaged by an old campaigner who had drifted from the public eye.

Former Prime Minister Gordon Brown had quietly rejoined the Labour Party ranks after his defeat by Mr. Cameron in 2010 and rarely made headlines.

Now, though, Mr. Brown, a Scot, catapulted himself into the referendum campaign to staunch the tide of Labour Party supporters deserting the party and joining "yes." He set out an ambitious timetable for delivering the Scottish parliament new powers that the three leaders quickly endorsed.

Summoning a fiery, patriotic and left-wing rhetoric that had almost disappeared from mainstream British politics, Mr. Brown harangued the nationalists in town hall after town hall and appealed to Scots to stand together with their neighbors elsewhere in Britain.

Pro-union supporters react as Scottish independence referendum results come in at a Better Together event in Glasgow on Friday. Agence France-Presse/Getty Images

"Let us tell people of what we have done together," Mr. Brown declared in the final days of the campaign in a Glasgow suburb, citing the U.K.'s wartime resistance of Hitler and the postwar construction of its welfare state.

"We did all this without sacrificing within the union our identity, our culture, our tradition as Scots," Mr. Brown said. "Our Scottishness is not weaker, but stronger as a result."

As polling day approached, Better Together's leaders broadened their campaign, mixing dire economic warnings with emotional pitches. Mr. Cameron warned Scots that a divorce from the U.K. would be painful and irreversible. He told them that a breakup of the union would be heartbreaking. Business leaders who had largely stayed silent joined the fray, warning of the economic hit Scotland could suffer if it left the U.K.'s embrace.

On a damp and misty polling day, the "no" camp's relentless assault finally paid off. Experts say that although more people voted Thursday than in any previous U.K. poll, the downfall of the "yes" campaign was its failure to mobilize all its supporters to turn out to vote.

"It's turnout that's crucial," said Mark Diffley, research director at pollster Ipsos-Mori.

Turnout in pro-independence Glasgow was 75%, a high number, but well short of the 85% recorded overall and turnouts in excess of 90% recorded in unionist strongholds such as Stirling. The "yes" side won only four of 32 districts.

—Cassie Werber and Nicholas Winning contributed to this article.

Write to Jason Douglas at jason.douglas@wsj.com, Jenny Gross at jenny.gross@wsj.com and Max Colchester at max.colchester@wsj.com