Britain will take an unprecedented step into the unknown on Wednesday with the first formal move towards leaving the European Union, starting a two-year process that has already divided the country.
Tens of thousands of people took to the streets of London on Saturday to protest against Brexit, and Scotland's parliament on Tuesday is set to vote in favour of holding an independence referendum.
Scots voted to stay in the EU but the majority verdict in Britain's EU referendum last year was 52 percent in favour of putting an end to a loveless marriage that has lasted more than four decades.
Those in favour are impatient for Brexit talks to begin and accuse Prime Minister Theresa May of playing for time since the June referendum.
But europhiles are increasingly concerned.
"Stop this madness!" read a banner held up at Saturday's march to parliament -- held just three days after a terror attack there -- to coincide with the 60th anniversary of the EU's founding treaty of Rome.
Prime Minister Theresa May's formal letter of notification to EU President Donald Tusk will trigger Article 50 of the EU's Lisbon Treaty: an exit clause that no member state has ever used.
The EU is expected to issue a first response later this week, followed by a summit of EU leaders on April 29 to adopt guidelines for the talks.
The exit negotiations themselves are not expected to start until at least three weeks after that.
The referendum campaign created bitter rifts between different parts of the country, generations and social classes, as well as exposing a chasm between the haves and have-nots of globalisation.
Brexit has also sparked a round of soul-searching in the European Union, even fears of a wider break-up.
EU leaders at a summit on Saturday adopted a declaration that enshrines for the first time a so-called "multi-speed" Europe, in which some countries can push ahead on key issues while others sit out.
- 'No deal' scenario -
May has said she will respond to a major demand of the Brexit campaign by cutting the numbers of EU immigrants who move to Britain -- hundreds of thousands every year -- and will have to pull Britain out of the European single market to do so.
She has advocated a "clean break" but has also said she wants an "implementation phase" to keep the status quo between Britain leaving the EU and any new arrangement to allow her country to adapt.
As the countdown begins, there is a real chance that negotiations will break down and Britain will be forced out of the EU without any deal in place.
Anand Menon of the UK in a Changing Europe research group estimated a 50-percent possibility of this happening, meaning Britain and the EU will have to trade with higher tariffs than now under World Trade Organization membership rules.
"A deal will take a lot more time, goodwill and tact than has been on display from either side," he said.
Business leaders have warned that this would be by far the worst scenario but May has said that "no deal is better than a bad deal" and she has the support of pro-Brexit hardliners in her Conservative Party.
- Stage is set -
The EU says "everything is ready" for Britain to begin its EU exit and officials in Brussels have already outlined a divorce bill for Britain of between 55 and 60 billion euros ($59 and $65 billion).
"When a country leaves the union there is no punishment, there is no price to pay to leave. But we must settle the accounts, no more, no less," the EU's chief negotiator Michel Barnier said on Wednesday.
Britain could get away with not paying anything, according to a recent report published by the House of Lords, but doing so would severely undermine its credibility.
The real question will be how much it will pay.
London also wants guarantees on the status of more than a million Britons living in other parts of the European Union, using the status of some three million EU citizens in Britain as a bargaining tool.
The trickiest part of the negotiations will be on trade relations, which could take years to work out.
Former WTO chief and European commissioner Pascal Lamy warned about the complexity of the Brexit process last week, likening it to "removing an egg from an omelette".