Boris Johnson will hail the “dawn of a new era” as the UK leaves the European Union.
At 11pm on Friday, bonds dating back to 1973 when the UK joined the European Economic Community will be broken, but the Prime Minister insists Brexit marks “not an end but a beginning”.
Very little will change at the moment of Brexit as a result of the deal which Mr Johnson agreed with Brussels and the 27 remaining member states.
But the UK faces further uncertainty as both sides seek to strike a trade deal by the end of the year.
In a symbolic move, Mr Johnson will chair a meeting of his Cabinet in Sunderland, the city which was the first to back Brexit when results were announced after the 2016 referendum.
And in what Number 10 billed as an “address to the nation” released an hour before the moment the UK leaves the EU, Mr Johnson will attempt to sound an optimistic note about the future and promise to heal the divides which have been caused in the bitter Brexit battles.
He will say: “Our job as the government – my job – is to bring this country together and take us forward.”
He will call Brexit “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 dawn of a new era in which we no longer accept that your life chances – your family’s life chances – should depend on which part of the country you grow up in.”
The address was being filmed by Downing Street rather than one of the national broadcasters in the latest clash between Number 10 and the media.
Traditionally, speeches by the PM in Number 10 have been recorded by a single broadcaster and then shared with other television networks, in what is known as a “pool” system.
As 11pm arrives, Big Ben will remain silent, despite a high-profile campaign fuelled by Mr Johnson, for repair works to be halted to allow Parliament’s bell to ring.
But on Parliament Square, Brexiteers will gather for a party led by Nigel Farage, while Union flags are already flying around Westminster.
In official events, Downing Street will be illuminated with a light show and a new 50p coin will enter circulation.
In Brussels, the UK flag will be removed from the EU institutions, with one Union flag expected to be consigned to a museum.
The Belgian capital has already dressed its famous Mannekin Pis statue of a urinating boy in a John Bull costume, complete with Union flag waistcoat.
In Scotland, which voted to stay in the EU in the 2016 referendum, candlelit vigils are planned.
The Leave a Light On gatherings are taking place in Aberdeen, Dundee, Glasgow, and Stirling, among other locations, and participants intend to send a message to the EU to keep open a place for Scotland.
In Northern Ireland, the campaign group Border Communities Against Brexit is to stage a series of protests in Armagh, near to the border with the Republic of Ireland.
Labour leader Jeremy Corbyn said Brexit left Britain “at a crossroads”.
There could be an “internationalist, diverse and outward-looking Britain” or one that will “trade our principles, rights and standards to secure hastily arranged, one-sided, race-to-the-bottom trade deals with Donald Trump and others”.
Mr Corbyn said: “We will resist a toxic Trump deal that puts our NHS, food standards and jobs at risk.
“That choice of which path we take for a post-Brexit Britain now lies before us.
“As we leave the European Union, whatever side we took in the Brexit debate, we now need to bring the country together to shape our common future, work to rebuild and strengthen our communities, and eliminate poverty and injustice in our society.”