At the outset of a bruising campaign, Prime Minister David Cameron tried a "stay the course" message, arguing that his Conservative Party had brought economic growth back to Britain by sticking to its austerity plan, however painful it might be.

When that pitch faltered and polls showed his party stagnating, Cameron changed course and found an approach that seemed to click.

He focused instead on a dire warning: He said the surprising strength of the separatist Scottish National Party might give it a share in the national government if the Labour Party scored well enough to form a governing coalition with the Scottish nationalists. That, he said, spelled ruin because it would bring to power a separatist party determined to break up the United Kingdom in the name of Scottish independence.

That argument, amplified daily by Conservative-friendly tabloids, helped Cameron carry the day. Not only did the Scottish nationalist surge in Scotland wipe out several dozen Labour seats in Scotland, greatly weakening party leader Ed Miliband's hopes of gaining power, it also gave Cameron's warnings resonance with English voters who did not want to see the SNP gain influence in the British Parliament.

Labour Party grandee Jack Straw, leaving Parliament after 36 years that included several Cabinet stints, said there was a "late surge" for the Conservatives in England and Wales and a complete Labour Party failure in Scotland.

"It is grim," he said. "It's an unbelievably bad situation in Scotland which frankly nobody anticipated. Obviously the whole party will have to reassess after the desperate situation in Scotland and the depressing situation in England and Wales."

He said voters who had been looking elsewhere returned to the Conservative fold in the campaign's final days, but there was no corresponding return to Labour.

The Scottish nationalist landslide gutted Labour's chances, reflecting a tectonic shift in sentiments there. Throughout the campaign, Scottish voters told pollsters and journalists they were tired of being taken for granted by Labour, and many had not been impressed when Miliband joined forces with Cameron to urge Scottish voters to reject independence in a September referendum. Scots whose families had for decades voted Labour turned away in droves.

There is irony here: Cameron and his party have long been extremely unpopular in Scotland, but he managed not only to triumph in his bid to keep the United Kingdom together with the "No" vote on independence in September, he also benefited greatly from the fallout from that vote, which proved so damaging to Labour.

The Liberal Democrats, meanwhile, lost most of their 56 seats, a devastating blow for the junior partner of the governing coalition.

The party had carried the banner of hope, change and honesty in the 2010 election, and has paid a heavy price for party leader Nick Clegg's about-face on raising tuition fees and other issues.