A new era has begun for the United Kingdom after it completed its formal separation from the European Union.
The UK stopped following EU rules at 23:00 GMT, as replacement arrangements for travel, trade, immigration and security co-operation came into force.
Boris Johnson said the UK had “freedom in our hands” and the ability to do things “differently and better” now the long Brexit process was over.
French President Emmanuel Macron said the UK remained a “friend and ally”.
UK ministers have warned there will be some disruption in the coming days and weeks, as new rules bed in and British firms trading with the continent come to terms with the changes.
Officials have insisted new border systems are “ready to go” amid fears of hold-ups at ports.
The UK officially left the 27-member political and economic bloc on 31 January, three and half years after the UK public voted to leave in the 2016 Brexit referendum.
But it has stuck to the EU’s trading rules for the past 11 months while the two sides negotiated their future economic partnership.
After trade talks went down to the wire, a landmark treaty was finally agreed on Christmas Eve. It became law in the UK on Wednesday after it was approved by Parliament.
Under the new arrangements, which came into force at 24:00 CET, UK manufacturers will have tariff-free access to the EU’s internal market, meaning there will be no import taxes on goods crossing between Britain and the continent.
But it does mean more paperwork for businesses and people travelling to EU countries while there is still uncertainty about what it will happen to banking and services, which are a major part of the UK economy.
Mr Johnson – who was a key figure in the Leave campaign during the 2016 referendum and who took the UK out of the EU in January six months after becoming prime minister – said it was an “amazing moment” for the UK.
In his New Year message, the PM said the UK was now “free to do things differently, and if necessary better, than our friends in the EU”.
“We have our freedom in our hands and it is up to us to make the most of it,” he said.
Lord Frost, the UK’s chief negotiator, tweeted that Britain had become a “fully independent country again” while veteran Conservative MP Sir Bill Cash said the outcome was a “victory for sovereignty and democracy”.
But opponents of Brexit maintain the country will be worse off than it was while in the EU.
Scottish First Minister Nicola Sturgeon, whose ambition it is to take an independent Scotland back into the EU, tweeted: “Scotland will be back soon, Europe. Keep the light on.”
Ireland’s Foreign Minister Simon Coveney said it was “not something to celebrate” and the UK’s relationship with Ireland will be different from now on, but “we wish them well”.
British firms exporting goods to the continent will have to fill out customs declarations straight away.
But checks on goods entering Britain from the continent will be phased in over a six-month period up to July 2021, although some new customs procedures have already come into force, on imports of alcohol, tobacco, chemicals and controlled drugs.
The first customs checks at the Eurotunnel following the UK’s departure from the single market went smoothly, the company said.
Spokesman John Keefe said: “It all went fine, everything’s running just as it was before 11pm. It’s very, very quiet, there are very few trucks around, as we predicted.”
In other major breaks from the past, the European Court of Justice will cease to have any role in deciding disputes between the UK and EU.
And the UK will gradually be able to keep more of the fish caught in its own waters.
Unlike the rest of the UK, Northern Ireland will continue to follow many of the EU’s rules, as its border with the Republic of Ireland remains all but invisible. The UK government said on Thursday online retailers in Britain will not have to make customs declarations when sending parcels to customers in Northern Ireland.