Scotland: It was a battle of the barnstormers overnight, as the heavyweights of the Yes and No campaigns pulled out all the rhetorical stops for the final bout of the Scotland independence referendum.

The opening punch was thrown by former UK prime minister Gordon Brown, who delivered what social media quickly dubbed "the speech that saved the Union", to a meeting of No campaigners in Glasgow.

"What we have built together, by sacrificing and sharing, let no narrow nationalism split asunder ever," an emotional, rough-voiced Mr Brown told the rally.

But up in Perth a relaxed, confident first minister Alex Salmond delivered his counterpunch, smiling and joking as he told a raucous rally of flag-waving nationalists (fond of chanting "Yes we can") that independence would give them "the power to choose hope over fear, opportunity over despair".

"We can write a new chapter in the story of this ancient nation."

The new nation could take on job-creating powers and enshrine social justice principles, he said.

And he warned that the No campaign would throw the kitchen sink "and the rest of the house" at voters until the very last hour of polling.

In recent weeks Mr Brown had become the spearhead of the No campaign, leading many to wonder why he was called into action so late.

He called upon the memory of two world wars and the comradeship between soldiers from the British nations.

"We not only won these wars, we built the peace together," he said.

He urged the Scots not to "throw the idea of solidarity into the dust" but to proudly declare that "we who vote 'No' love Scotland and love our country."

"The vote on Thursday is not about whether Scotland is a nation - we are, yesterday, today and tomorrow.

"It's not about whether there is a Scottish Parliament - we have it after a referendum 10 years ago. It's not about whether there are increased powers, we are all agreed to increase the powers.

"The vote tomorrow is whether you want to break and sever every link, and I say let's keep our UK pension, let's keep our UK pound, let's keep our UK passports, let's keep our UK welfare state."

He dismissed the Yes campaign with a scornful "they do not know what they are doing – they are leading us into a trap".

Mr Brown is crucial to the No campaign because he commands the respect of many Scottish Labour voters, a group the nationalists have worked hard to woo.

Jane Merrick, political editor of the Independent on Sunday, said the speech was "spine-tinglingly good", and Mr Brown was "rewriting his political (and actual) obituary."

But on Wednesday evening, barely 24 hours before the polls were due to close and counting begin, it was Alex Salmond's turn to fire one last salvo for Yes.

At City Hall in Perth he told the crowd they had mounted "the greatest campaign in Scottish democratic history".

"You've already made Scotland a much better place," he said.

"This is the opportunity of a lifetime and we must seize it with both hands," he said.

Mr Salmond took a swipe at the "Westminster establishment… the powerful few who believe they always know what is best - that power should always be in their hands."

He reminded the crowd of the many nations at the Commonwealth Games in Glasgow, once British subjects, "rich and poor, large and small, and not one of them has any intention of going back."

At one point he even got a cheer for mentioning 18th-century philosopher and economist Adam Smith.

But the biggest cheer was reserved for his promise to "remove the obscenity of weapons of mass destruction" – the Trident nuclear weapons currently based in Scotland.

He admitted that 'Yes' were the underdogs and asked undecided voters to trust in Scotland – "who better to meet (our) challenges than the people who live and work in this nation?"

And Mr Salmond also sent a message to the so-called 'rUK' (the rest of the UK) after Scotland left, assuring them that Scotland would wanted to build a "new, better, harmonious" relationship with them.

"In an independent Scotland you will find your closest friend, most honest counsel and most committed ally," he said.

"What we seek is a relationship of equals to our mutual advantage."

To the people of Scotland, he said those who were given this moment "should not let it pass them by".

"Don't let them tell us we can't. Let's do this now."

Mr Salmond, who turns 60 at the end of the year, has publicly insisted he will serve out his full term to 2016, however there are persistent rumours that a 'No' vote would bring forward his retirement.

Mr Salmond's warm-up act, deputy leader Nicola Sturgeon, told the crowd she had never seen such an "energised, enthused, informed and inspired" electorate.

She also called for unity, saying she had met wonderful people who would vote Yes, and wonderful people who would vote No.

"On Friday we become one country moving forward, united together," she said.

The final polls before Thursday's vote had No narrowly in front, but by a margin less than the margin of error, and less than the number of undecideds.

Pollsters admitted that it was simply impossible to predict the result.

The polls open 7am Thursday, local time, and close at 10pm (7am on Friday on Australia's east coast).

Counting will go through the night, and the result may not be known until 7am Friday: mid-afternoon in Australia.