London/Brussels - According to the most pessimistic forecasts, Saturday, March 30, 2019 could be one of the most chaotic days in Europe's post-war history - if Britain leaves the European Union without an agreement in place.
The notion that this could happen was long seen as virtually impossible, but time is running out.
Effects of Brexit
The talks in Brussels are still bogged down. Without a withdrawal deal, an agreement on a transitional period to the end of 2020 would lapse.
The effects could hit millions of people, both directly and indirectly.
Some say vehicle tailbacks could build up on both sides of the English Channel - where some 11,500 trucks cross every day.
Under World Trade Organization (WTO) rules - the default if no deal is agreed - all vehicles would have to be inspected, and customs duties imposed on many loads.
Essential medical supplies could run short in British hospitals, supermarket prices could soar as shelves empty of certain goods.
"Leaving the EU without a deal would cause major inconvenience to millions of pensioners, travellers and drivers," the Association of British Insurers said in a recent statement.
Will the politicians allow this to happen?
In the worst case, flights could have to be cancelled on both sides, because the legal basis for cross-border aviation would cease to be valid.
But Brexit Secretary Dominic Raab and other members of Prime Minister Theresa May's government, who are making contingency plans for a no-deal Brexit while insisting that they remain committed to securing an agreement, say such claims are nonsense.
The EU long worked on the assumption that a disorderly Brexit would have much worse consequences for Britain than for the remaining 27 members of the bloc, with its 450 million consumers.
But a no-deal scenario could also inflict significant damage on the EU.
Failure to reach a deal would also have political consequences for Ireland, which would have to introduce customs controls at the border with Northern Ireland - something that all sides say they want to avoid at all costs.
It could leave a hole in the EU budget of billions of euros, while London's pledge to pay some 40 billion euros (47 billion dollars) as a leaving settlement would be void.
Even supplies of donor sperm for IVF could dry up - Britain imports almost half of it sperm from Denmark.
Eurosceptic politicians waiting to celebrate Britain leaving the EU - the Brexiteers - say such claims are part of a second wave of "project fear," which they accused former prime minister David Cameron and other Remain supporters of mounting before the 2016 referendum.
But John Curtice, a political scientist at the University of Strathclyde, says the perceived economic consequences of Brexit have affected British public attitudes towards leaving the EU, apparently fuelling a small shift of voters from Leave to Remain.
Staying in the EU
The idea that Britain could be steering a course for turbulent economic waters has also helped cause "a discernible, if modest shift" in support for a second Brexit referendum, according to opinion polls, Curtice wrote this week.
Many opposition lawmakers, and some pro-EU Conservatives, have backed a growing People's Vote campaign, hoping to secure another referendum that many hope would result in Britain staying in the EU.
Simon Hix, a political scientist at the London School of Economics, believes a woolly, provisional Brexit is more likely than a no-deal one or an about-turn underpinned by a second vote.
"It increasingly looks like we're heading for a vague 'political declaration' on the future relationship, alongside the [withdrawal agreement] and transition deal," Hix tweeted on Thursday.
Details of future trade arrangements would only be agreed during the transition, Hix said, meaning Britain and the EU would formally separate in March with a face-saving deal for what other commentators have dubbed a "blind Brexit."