In a major shift in British politics, the Scottish Nationalists have displaced Labour as the largest party in the Scottish Parliament. This gives them the chance to form a coalition government. Their pledge to hold a referendum on Scottish independence will be the principal element in that bargaining.
Even if it is watered down into an options poll, as their likely partners the Liberal Democrats insist, such a prospect represents a radical change. It is the first time the SNP has emerged as the biggest party - and a forceful reminder that the last time Labour lost in Scotland was in 1955.
These Scottish elections are the main talking point from yesterday's results, but they should not overshadow similar trends away from Labour in the 60-member Welsh Assembly and the mid-term local elections in England. Commenting on them prime minister Tony Blair was upbeat yesterday - and with some justification. Governing parties always take a hit in them, he said, and this one is less than some governments have taken. Conclusions should not therefore be drawn from them about the likely outcome of general elections in two or three years time.
It is the standard incumbent response to such setbacks. But it is amplified on this occasion because of Mr Blair's imminent departure as prime minister, his likely succession by Gordon Brown and Labour's struggle to ward off a resurgent Conservative revival in England especially. The local elections bore out this last trend, showing high Labour losses throughout city and county councils. National trends of unpopularity over Iraq, Labour's record in government and voter fatigue are at play here, adding real interest to British politics over the next three years.
The Scottish result is the most dramatic of these changes, even if it should not be over-interpreted at this stage. The swing against Labour is less than many expected, reflecting that party's vigorous campaigning of recent months. The SNP leader Alex Salmond is a doughty electoral fighter and a canny political leader with a fine sense of tactics. He will need all these skills to assemble a workable coalition capable of delivering concrete benefits from a Labour government in London led by Mr Brown. Most Scots remain to be convinced that independence would work to their advantage, as distinct from a deeper, more federal type of devolution favoured by the Liberal Democrats.
Nevertheless a new political agenda has been forged in Scotland, and in the UK as a whole. Its future identity as a united polity has been put in question by this result.