While recent opinion polls have swung slightly back toward the "no" camp, there remains a distinct possibility that Thursday's Scottish referendum will trigger a previously unthinkable breakup of Britain.
If this were to happen, the biggest risks for global businesses and investors do not lie in the economic problems created by Scotland's choice of currency or the inevitable arguments about sharing North Sea oil revenue and the British national debt. These are crucial challenges for Scotland and have been much discussed in financial institutions and think tanks. But the crucial issue for the world economy and financial markets is about the resulting impact on the European Union - and especially on Britain, which would remain the world's sixth largest economy even if Scotland departs.
These political risks, which I discussed in my last column, can be broken down into four questions: What would Scottish independence, if it happens, mean for British politics and economic management over the nine months, until the May 2015 general election? What effect would it have on the election results? How would all this turmoil affect Britain's fraught relationship with Europe? Would Scottish independence act as an inspiration for secessionist movements in other European countries?
Britain's Prime Minister David Cameron speaks during a visit to the Scottish Widows building in Edinburgh, Scotland The answers to all four questions promise to be more destabilizing than almost anyone would have predicted a month ago.
Starting with the issue of other European independence movements, the answer is obvious. If Scotland votes for independence, it would become extremely difficult for the Spanish government to continue denying a similar democratic right to the Catalans and Basques. Beyond that, Flemish separatists would intensify pressure in Belgium, and the Northern League in Italy could get a new lease on life.
Focusing back on Britain, the political implications become more complex. If Britain breaks up after Thursday's vote, Prime Minister David Cameron would have to take responsibility for promoting the referendum on needlessly risky conditions that in hindsight look downright reckless.
It was Cameron who decided to offer the Scots a simple choice between staying in the union or breaking it - instead of taking up the Scottish National Party's proposal for a third option of increasing self-government within Britain. Cameron also allowed preserving the union to be presented as a negative option in the phrasing of the referendum question and accepted the National Party's controversial decision to lower the voting age from 18 to 16.
For all these reasons, plus his unpopularity in the Conservative Party's powerful anti-European wing, Cameron would likely face huge pressure to resign if the referendum passes.
The Conservative Party has a history of turning suddenly and ruthlessly against its leaders. In September 1990, nobody imagined that Prime Minister Margaret Thatcher was even remotely vulnerable. Less than three months later she was gone.
'No Thanks' badges are displayed during campaigning by Alistair Darling, the leader of the campaign to keep Scotland part of the United KingdomWhether or not Cameron is ousted after the vote, the British government would be reduced to lame-duck status until the May election. The only issues on the political agenda would be the terms of Scottish separation and the Cameron government's astonishing complacency about presiding over national breakup.
This complacency, which voters, investors and businesses have only just started to notice, was exemplified on Monday when Sir Jeremy Heywood, head of the British Civil Service, calmly told a shocked parliamentary committee that government departments were doing absolutely nothing to prepare for the possibility of Scottish independence.