If the laws of basic arithmetic applied,Boston should be the happiest little town in Britain right now. It was here that three in every four voters stormed the ballot box in 2016 and demanded a split from the European Union. Fuelled by a potent cocktail of anti-immigration sentiment and anger over government austerity measures,the revolution was so overwhelming that Boston ended up recording the highest pro-Brexit vote in the United Kingdom.

Nearly four years later,the unassuming Lincolnshire market town three hours north of London has finally got its way:the UK will formally leave the EU at 11pm on Friday,January 31.

British Prime Minister Boris Johnson plans to mark the moment by addressing the nation with his trademark optimism from Downing Street. The country's ruling Conservative Party opened online sales for a limited edition £15 ($24.60)"I got Brexit done"coffee mug. Giant Union Jack flags have been strung above The Mall between Buckingham Palace and Trafalgar Square. And in the European Parliament,outgoing British members were farewelled with a spontaneous rendition ofAuld Lang Syne.

"Only in the agony of parting do we look into the depth of love,"said a beaming European Commission president Ursula von der Leyen,quoting British novelist George Eliot."We will always love you and we will never be far. Long live Europe!"

But in Boston,the mood is less celebratory.

"People aren't exactly overjoyed,"says local mayor Anton Dani,a cafe owner who joined the UK Independence Party following a chance handshake with Brexit agitator Nigel Farage but later switched to the Conservatives.

"We might be leaving on January 31 but that is just the start of it. We still don't know what Brexit will actually look like. People who supported Brexit are also worried that it will not be delivered on time.

"Boston and other parts of England voted the way[they] did because of the impacts of migration and the pressures of immigration on infrastructure. Leaving the EU on January 31 doesn't automatically solve those concerns for Leave supporters."

It's also a fairly unhappy scene on the other side of the fence. Asked to nominate which stage of"grief"they were in,only 30 per cent of Remain voters told pollster YouGov that they had now accepted the 2016 referendum result. The rest were wallowing in"depression","anger"and"denial". And 3 per cent still thought Brexit could still be stopped.

"The results show that many Remain voters still haven’t come to terms with the decision,"says the polling firm's Matthew Smith.

Britain's formal departure is the biggest milestone yet in the decade-long Brexit battle that has torn the country apart,given new momentum to Scottish independence,claimed the political careers of Conservative prime ministers David Cameron and Theresa May and shaken international faith in the UK as a modern global power.

Guy Verhofstadt,the European Parliament's Brexit coordinator,put it this way:"It’s sad to see a nation leaving - a great nation - that has given us so much:culturally,economically,politically,even its own blood in two world wars. It’s sad to see the country leaving that liberated Europe twice."

There is,though,a palpable sense of relief in Britain thatJohnson's thumping December election win has brought an end to the parliamentary paralysis that threatened to sink Brexit entirely. His victory rewrote the political map by flipping pro-Leave,blue-collar constituencies in England's north firmly into the Tory column. The circuit-breaker poll has washed away some - but not all - of the anxiety and anger that had infected the British public.

But the split has also thrown the UK headfirst into a new era of uncertainty. Britain is conducting a national exercise in patience as it waits to see what the fine print of the separation from Europe looks like,and whether the terms meet,exceed or fall short of the expectations of the people of Boston and 17.4 million others who voted to abandon the EU experiment.

Johnson,a shrewd operator who has been one of the few politicians to capitalise on the turmoil,has sensed the division that still exists in Britain. Having initially suggested Big Ben could toll to mark the 11pm departure,the notorious stunt master has increasingly toned down the jubilant rhetoric.

"Our job as the government - my job - is to bring this country together and take us forward,"Johnson will say in his speech."And the most important thing to say tonight is that this is not an end but a beginning. This is the moment when the dawn breaks and the curtain goes up on a new act.

"It is a moment of real national renewal and change. This is the moment when we begin to unite and level up."

A December opinion poll for Ipsos MORI detects the early signs of"changing public priorities for 2020"as Britain's troubled public health system overtakes Brexit as the biggest issue worrying voters.

But in a sign of anxiety over the possible outcomes of the transition period,the percentage of people who rank Brexit as a top issue is still at near-record levels and even larger than at the height of the divisive 2016 referendum itself.

"Brexit is subsiding as an issue to some degree,but it is clearly still a really big one for the public,"says Mike Clemence,a researcher at Ipsos MORI.

The UK and EU are now effectively a divorced couple still living under the same roof while they sort out who gets what. All aspects of the existing relationship continue for an 11-month transition period as officials from both sides scramble to strike new agreements covering trade,security,immigration and a myriad of other complex issues by a hard deadline of December 31,2020.

"The negotiation task is huge,"warns Institute of Government senior researcher Maddy Thimont Jack.

"'Taking back control'was the slogan of the referendum campaign but what that means is actually having to set up entirely new domestic policies in areas like agriculture,fisheries and the environment and get the UK ready for managing those areas at the end of a relatively short transition period,"she says."There has been a realisation that this is all more difficult than people had first thought."

The two most likely options by the end of this year's transition period are a bare bones goods-only trade agreement,or no agreement at all. Commonwealth Bank analysts point to Bank of England projections of a 0.75 per cent dip in GDP by the end of 2023 under a basic agreement,and a whopping fall of between 2.5 and 8.5 per cent down should there be no deal. The stakes are high.

"There's a question about whether the can has just been kicked down the road,"says Australia-UK Chamber of Commerce chief executive Catherine Woo."Given we'll be in that transition period until the end of the year,I think the psychological impact of leaving ... is softened and people are already thinking ahead to whether we are headed to a cliff edge on the 31st of December."

Woo says"lingering conservatism"on spending is likely until the outcome of"fraught negotiations ahead"become clear but predicts Johnson's election win will see capital released in 2020 that had been held back during years of political uncertainty.

She points to other positives on the horizon,including animpending free trade agreement between Australia and the UK that will be thrashed out this year and implemented in 2021.

Alex Dawson,a senior adviser to May during her stint in Downing Street,says the technical and political debate about trade will"mostly take place in the background of national consciousness but that has the potential to explode into relevance in future".

"The free trade agreement talks with the EU,the US,Japan and Australia could change the rules around entire sectors of the UK economy at the stroke of a pen,"Dawson says."This impact of these deals should not be underestimated by the Westminster class as they could easily determine whether future generations see Brexit as a success or a failure."

London's business community is also eagerly waiting smoke signals from Downing Street about what the country's new immigration scheme will look like. Johnson is pledging to make it easier to bring in exceptional labour talent,howevera clampdown on migration and labour rights looms amid community concerns about the impact of the EU's free movement regime.

Between 2001 and 2018,the share of EU workers employed in Britain almost tripled to 7 per cent and the share of non-EU migrant workers increased to just over 10 per cent. At the same time,the population share of the UK-born fell by more than six percentage points but the EU-born population in Britain doubled to 5.5 per cent.

In Boston,national statistics estimates suggest up to 30 per cent of the town's 68,000-strong population could be from overseas,particularly from eastern European EU member states such as Lithuania,Poland and Romania. At the last census in 2011,that figure was about 15 per cent. And a decade before that,it was about 3 per cent.

"Yes,we need people to come and add to our town but we don't want the town to be destroyed at the same time,"says Dani,the mayor."People felt enough is enough. Hospitals haven't been built,schools haven't been built.

"The biggest problem now though is that people in England have lost faith in governments. Whether that changes after Brexit happens,we have to wait and see."