Video report by ITV News Correspondent Dan Rivers
Big Ben has marked the moment the UK leaves the EU’s single market and customs union.
The famous bell sounded at 11pm UK time - 12 midnight in Europe - to signal the end of Britain's near 50-year ties to Brussels.
The political squabble over Brexit cost two prime ministers their job before Boris Johnson delivered on his 2019 election pledge to "get Brexit done".
In his new year message, the Prime Minister reflected on the past 12 months during which “we lost too many loved ones before their time” because of the pandemic.He also hailed his Brexit deal, saying: “This is an amazing moment for this country. We have our freedom in our hands and it is up to us to make the most of it."
The House of Commons authorities have said the bell will also ring at midnight to see in 2021.
ITV News Political Correspondent Paul Brand explains what's next
The first customs checks at the Eurotunnel following the UK’s departure from the single market have gone smoothly, the company said.
Spokesman John Keefe told the PA news agency: “It all went fine, everything’s running just as it was before 11 o’clock.
“It’s very, very quiet, there are very few trucks around, as we predicted.”
The first arrivals on the shuttle from France following the end of the Brexit transition period are expected at around 12.23am.
ITV News Europe Editor James Mates has reaction from Calais
The famous bell has been largely silent since 2017 owing to repairs on the clock and Parliament’s Elizabeth Tower in which it is housed, only being reconnected for significant occasions.
The bell, which weighs 13.7 tonnes, last rang on November 11 to mark Armistice Day.
Members of the public have been urged to stay away from Westminster on New Year’s Eve owing to coronavirus restrictions.
The bell was tested in the days leading up to New Year’s Eve to ensure it could produce its 12 bongs when the clock strikes midnight.
One of the tests will be an hour before midnight, which coincides with the end of the Brexit transition period.
There was a row earlier this year as Brexiteers tried and ultimately failed to get the bell to ring in the moment the UK left the European Union on January 31.
January 1 will mark the end of a political journey triggered by the referendum on European Union membership in June 2016.
While many experts warn of the economic impact of Brexit – even with a deal – Mr Johnson said the UK's destiny “now resides firmly in our hands”.
The prime minister said: “I want to thank my fellow MPs and peers for passing this historic Bill and would like to express my gratitude to all of the staff here in Parliament and across Government who have made today possible.
“The destiny of this great country now resides firmly in our hands. We take on this duty with a sense of purpose and with the interests of the British public at the heart of everything we do.
“11pm on the 31st December marks a new beginning in our country’s history and a new relationship with the EU as their biggest ally. This moment is finally upon us and now is the time to seize it.”
The prime minister’s optimism has not been shared across the board, with Confederation of British Industry (CBI) Director General Tony Danker warning businesses are in the dark.
Among the issues are firms having "no idea" how Europe will police its borders from, he said.
Mr Danker urged the government to put pressure on the EU to provide clarity on the borders issue, and told ministers they must turn the more than 1,200 page 'Trade and Co-Operation
Agreement' into "practical guidance" for firms.
Mr Danker said: "Up until Christmas, most businesses in the country had done all they possibly could do to prepare for whatever the eventuality was.
"But then on Christmas Day we had 1,200 pages of legal text come down the chimney and I have to tell you, it really changes the nature of our trading relationship with the EU.
"So at this stage, with three days to go, we urgently need that legal text turned into practical guidance."
So what is and isn't in the deal?
Boris Johnson said the deal covers trade worth around £660 billion and that it is a "good deal for the whole of Europe", which means:
Goods and components can be sold without tariffs and quotas in the EU market.
It will allow the share of fish in British waters that the UK can catch to rise from around half now to two-thirds by the end of the five-and-a-half year transition.
Allegations of unfair competition will be judged by an independent third-party arbitration panel with the possibility of a “proportionate” response.
The Erasmus student exchange programme will be replaced in the UK by a worldwide scheme named after code breaker Alan Turing.
However, on financial services, a vitally important sector to the UK, Mr Johnson conceded he had not got all he wanted.