Prime Minister David Cameron is calling on the people of England, Wales and Northern Ireland to send a message to Scotland as it prepares to vote in the independence referendum: "We want you to stay."
In a speech at the Olympic Park in London, Mr Cameron will summon up the spirit of patriotism of the 2012 Games as he argues that the whole country will lose if Scotland votes to leave the UK.
While accepting that the decision on September 18 is a matter for Scots alone, Mr Cameron will urge the English, Welsh and Northern Irish to do whatever they can to influence the outcome, telling them: "You don't have a vote, but you do have a voice."
The keynote speech is Mr Cameron's most high-profile intervention in a referendum campaign in which he has repeatedly stated his passionate desire to preserve the Union but has refused to debate with Scottish First Minister Alex Salmond.
Independence would be bad for Scotland but would also leave the United Kingdom "deeply diminished" and would "rip the rug from under our own reputation" in the world, Mr Cameron will say.
With seven months to go to the poll, the outcome remains "up in the air", the Prime Minister is expected to say. There must be no complacency among those supporting the preservation of the Union, who must do "whatever it takes" to persuade the Scots to vote "No" to separation.
At a location carefully chosen to symbolise the successes of the whole United Kingdom working together as "Team GB", Mr Cameron will say that the Olympic medals were won under the banner of a Union flag that was not only red and white but also blue. And he will say: "It's Team GB I want to talk about today - our United Kingdom."
He will stress that the decision on independence is "squarely and solely for those in Scotland to make", saying: "It is their choice, their vote".
But he will add: "My argument today is that though only four million people can vote in this referendum, all 63 million of us are profoundly affected.
"There are 63 million of us who could wake up on September 19 in a different country, with a different future ahead of it.
"That's why this speech is addressed not to the people of Scotland, but to the people of England, Wales and Northern Ireland...
"We would be deeply diminished without Scotland. This matters to all our futures. And everyone in the UK can have a voice in this debate."
Mr Cameron will argue that the UK is a "powerful brand" in the modern world, with a global reputation for being "unique, brilliant, creative, eccentric, ingenious".
And he will warn: "If we lost Scotland, if the UK changed, we would rip the rug from under our own reputation. The plain fact is we matter more in the world together."
Warning that the result on September 18 cannot be taken for granted, Mr Cameron will say: "We have just seven months to go. Seven months to do all we can to keep our United Kingdom as one. Seven months to save the most extraordinary country in history. And we must do whatever it takes.
"So to everyone in England, Wales and Northern Ireland, everyone - like me - who cares about the United Kingdom, I want to say this: you don't have a vote, but you do have a voice.
"Those voting are our friends, neighbours and family. You do have an influence.
"Let the message ring out from Manchester to Motherwell, from Pembrokeshire to Perth, from Belfast to Bute, from us to the people of Scotland.
"Let the message be this: We want you to stay."
Scotland's Deputy First Minister Nicola Sturgeon has accused David Cameron of a "shameful" bid to use the Olympics as a "political tool" on the day the 2014 Winter Games begin in Russia.
The Prime Minister's intervention was a sign of "jitters" in the No camp in the face of polls showing growing enthusiasm for independence, she claimed.
Ms Sturgeon said: "This is a cowardly speech from a prime minister who uses the Olympic Park in London to give high-handed lectures against Scotland's independence but hasn't got the guts to come to Scotland or anywhere else to make his case in a head-to-head debate.
"David Cameron, as the Tory Prime Minister, is the very embodiment of the democratic case for a Yes vote for an independent Scotland - and he knows it.
"A Yes vote will put Scotland's future in Scotland's hands, and will mean we will never again have to endure Tory governments, prime ministers and policies we didn't vote for."
She added: "As for using the Olympic stadium on the day the Winter Olympics begin and seeking to invoke the successes of London 2012 as an argument against Scotland taking its future into its own hands, it betrays the extent of the jitters now running through the No campaign.
"They see the polls closing and they are clearly rattled - but to politicise any sporting occasion is shameful.
"Unfortunately, with this tawdry bid to use the Olympic Games - past and present - as a political tool, David Cameron has exposed the utter hypocrisy and double standards at the heart of the No campaign."