Britain's Prime Minister David Cameron and wife Samantha smile as they arrive at party headquarters in central London. Photo / Steve Parsons
Second term will be challenging with Scotland and Europe top of agenda.
Two questions will dominate and define David Cameron's second term as Prime Minister: Will the United Kingdom survive in its current form? And will the UK remain a member of the European Union?
Scotland and the Union will be the most immediate concerns. The Scottish National Party did not run for election to the House of Commons on a promise of a second referendum on independence, but that vote is now firmly on the political agenda. Especially if the nationalists turn their seismic triumph at Westminster into another victory in the Scottish Parliament elections next year.
What can Cameron and his new Government do to keep Britain together? My guess is an early move to some form of constitutional convention that attempts to answer the call that Scots have made very loudly in these election results. It will also have to address the evident English sense of injustice over the current settlement.
What sort of changes could it make? Perhaps Scotland could get full autonomy over its own finances. Essentially, give the Scots everything they want except full independence.
And perhaps Britain could move to a fully federal system, meaning some form of English Parliament; senior Tories like Boris Johnson have said they are open to federalism.
Does that sound radical or dramatic? Yes, but these are extraordinary times: the most dramatic changes in the British constitution must surely be considered to avoid an even more dramatic and destructive outcome: Scottish independence.
And even if those dramatic measures are taken, there is no certainty of success. The breakup of Britain must now be considered a realistic possibility.
Then there's Cameron's promise of a referendum on EU membership, to be held by the end of 2017. Assuming he sticks to his preferred timetable, that vote will be in the second half of 2017. Debate over its outcome will dominate both domestic politics and British diplomacy, and loom large in many economic conversations too.
The result of the European referendum is also hard to call: exit must be considered a possibility. It's a decent bet that Cameron will campaign to stay in, but could that open up a historic split in the Conservative Party? It's another very real possibility.
Perhaps Cameron may seek to delay that EU referendum, perhaps arguing that until the Scottish question is resolved, Britain cannot seek to answer another fundamental question about its place in the world? Just a thought, but he would surely be tempted. Though quite what Tory backbenchers - who will have a lot more clout in this Government than the last one - would make of that is another matter.
Whatever the answer to those two fundamental questions about Britain's nature and place in the world, Cameron's second term will be far more consequential than his first, and quite likely one of the most significant premierships in recent history.
Results
With 631 of 650 seats declared. 323 seats needed for a majority.