The former Labour chancellor will stress the positive pro-Union case on the grounds of family and friendships, trade and the economy, as well as on the shared political, economic and cultural institutions that bind Scotland to the rest of the UK.
Launching the Better Together campaign in a lecture theatre at Edinburgh Napier University, Mr Darling will echo its slogan, saying: "The truth is we can have the best of both worlds; a strong Scottish Parliament and a key role in a strong and secure United Kingdom.
"The truth is, Scotland's future, our future and our families' future will be economically, politically and socially stronger as a partner in the United Kingdom. The truth is that this coming together of family, friends, ideas, institutions and identities is a strength, not a weakness. It is an ideal worth celebrating."
He will warn Scots that the choice they make on referendum day 2014 will be irrevocable. "If we decide to leave the United Kingdom, there is no way back. It is like asking us to buy a one-way ticket to send our children to a deeply uncertain destination."
Today, the No campaign will give out 500,000 leaflets at train stations across the nation, setting out 10 ways in which Scotland benefits from being part of the UK, and newspapers will carry full-page adverts with the campaign slogan "We want the best of both worlds" – in other words Scotland with its own distinctive parliament in a strong UK.
The No campaign has so far issued
three of the reasons not to vote for independence:
l That one in five workers in Scotland is employed by English firms.
l That thousands more work for the UK Government in places such as the Department for International Development offices in East Kilbride.
l That 800,000 Scots live and work in England and Wales "without the need for papers or passports".
Also today, Better Together will launch its own website run by Blue State Digital, which ran the successful online campaigns of US President Barack Obama and more recently advised on the web strategy of Francois Hollande's successful presidential campaign in France.
Just as the campaign against independence released a poll hours ahead of the start of the Yes Scotland launch last month, seeking to cast a shadow over it – it showed only one-third of Scots wanted independence – so this morning the pro-independence campaign issued its own poll, seeking to exploit what it regards as a major weakness – Labour's alliance with the Conservatives in the anti-independence camp.
The poll asked just two questions. The first was about trusting the UK Government to take the right decisions. Some 28% said they had a great deal or a fair amount of trust while 69% said they had little or no trust. The second asked would it be better for Scotland to be part of the UK when there was a Tory Government at Westminster. Some 20% agreed and 50% disagreed.
Meanwhile, Stewart Hosie, the SNP Treasury spokesman, yesterday gave the strongest hint yet that First Minister Alex Salmond was preparing to back a second question on the ballot paper.