LONDON (AFP) - Britain on Friday (Jan 31) ends almost half a century of integration with Europe, finally making its historic departure from the European Union to begin a new - but still uncertain - future, with emotions running high following years of wrangling and several false starts.

As the clocks strike 11pm (7am Saturday Singpore time) - midnight in Brussels - Britain becomes the first country to leave the 28-member bloc and will go it alone for the first time since 1973.

Prime Minister Boris Johnson has backed Brexit since the 2016 referendum vote to leave that triggered deep bitterness and division but he has promised to unite the country in a new era of prosperity.

"Our job as the government, my job, is to bring this country together and take us forward," Mr Johnson said in a statement to mark the occasion.

"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."

A 'SEA CHANGE'

German Chancellor Angela Merkel called Britain's departure a "sea change" for the bloc, although nothing will immediately feel different because of an 11-month transition period negotiated as part of an EU-UK exit deal ratified this week.

Britons will be able to work in and trade freely with EU nations until Dec 31, and vice versa, although the UK will no longer be represented in the bloc's institutions.

But legally, Britain is out - with no easy way back.

And while the exit terms have been agreed, Britain must still strike a deal on future relations with the EU, its largest trading partner, which sets out its negotiating position on Monday.

"We want to have the best possible relationship with the United Kingdom, but it will never be as good as membership," European Commission president Ursula von der Leyen said. "Our experience has taught us that strength does not lie in splendid isolation, but in our unique union."

YEARS OF TUMULT

Getting this far has been a traumatic process.

Despite Britain's resistance to many EU projects over the years - it refused to join the single currency or the Schengen free travel area - the 2016 vote to leave was a huge shock.

It unleashed political chaos in London, sparking years of bitter arguments that paralysed Parliament and forced the resignations of two prime ministers.

Mr Johnson brought an end to the turmoil with his decisive election victory last month, which gave him the parliamentary majority to ratify the Brexit deal.

But Britons remain as divided as they were nearly four years ago, when 52 per cent voted to leave and 48 per cent voted to remain in the EU.

Friday's newspapers reflected that continued split, with best-selling eurosceptic tabloid The Sun triumphantly declaring "our time has come" on its front-page alongside an image of Big Ben.

But pro-European The Guardian opted for the headline "small island", calling Brexit "the biggest gamble in a generation".

In Scotland, which backed remaining in the bloc in 2016, First Minister Nicola Sturgeon called it "a moment of real and profound and sadness... tinged with anger".

She vowed to step up the campaign for independence, which the Scots rejected in a vote in 2014.

PARTIES AND VIGILS

Mr Johnson, himself a polarising figure, has emphasised unity and is avoiding any major celebrations that might exacerbate divisions.

The Conservative leader was hosting a special Cabinet meeting in the north-eastern English city of Sunderland, which was the first to declare for Brexit in the 2016 vote.

At 10pm, he will broadcast an address to the nation, and then host a reception for staff at Downing Street, before a light show outside No 10.

Millions of commemorative 50p coins go into circulation.

Ex-MEP Nigel Farage, who has spent decades campaigning to leave the EU, is planning a large rally in nearby Parliament Square - one of several pro-Brexit parties being held around the country.

Pro-EU groups have planned candlelit vigils.

TRADE TALKS LOOM

British eurosceptics have campaigned for decades to free their country from what they see as an overly bureaucratic and unaccountable institution.

Mr Johnson has promised to leave the EU's single market and Customs union so Britain can strike trade deals around the world.

But exactly how that will work - and at what cost to firms that depend on EU business - is unclear.

The divorce deal resolved the issue of London's debts, the rights of EU expatriates, the status of Northern Ireland and the transition period.

But Mr Johnson has given himself just 11 months to negotiate a new partnership, covering everything from trade to security cooperation.

He will set out his plans in a speech on Monday but Brussels has already warned he must either limit his ambitions or ask for more time.

Irish Prime Minister Leo Varadkar warned on Friday that a failure to reach a post-Brexit trade deal by the deadline would pose an "existential threat" to Britain's nearest neighbour.

"So we do need that deal," he said.

Mr Johnson also wants a trade agreement with the United States, where President Donald Trump is a big Brexit backer.