With opinion polls suggesting the referendum remains too close to call, Cameron, the leader of the England-centric ruling Conservative party, is expected to try to appeal to Scots' emotions by likening the four-nation UK to a family.
"There's no going back from this. No re-run. If Scotland votes "yes" the UK will split and we will go our separate ways forever," he is expected to say, according to advance extracts given to local media by his office.
Cameron is likely to repeat the anti-independence "Better Together" campaign's core message: That inside the UK Scotland can have the benefits of belonging to a larger more influential entity while enjoying an ever increasing measure of autonomy.
He will make his intervention, expected during the second half of Monday, after David Beckham, the retired high-profile footballer, added his name to a petition of English celebrities who say they want the Scots to stay in the UK.
The celebrity group, "Let's Stay Together", is organizing a public rally on Monday evening in London's Trafalgar Square to appeal to Scots not to break up the United Kingdom.
On Sunday, thousands of independence supporters took to the streets of Scotland's largest city, Glasgow, as polls showed the rival camps running desperately close. REUTERS