SCOTLAND will make history today when an estimated 3.5 million people go to the polls to decide the country's future.

Polling stations across the nation have opened their doors after more than two years of debate and a month of intensive campaigning, as the polls continued to show the outcome on a knife-edge.

Alex Salmond made his final appeal to voters at an emotionally charged Yes campaign rally in Perth last night, after Gordon Brown rallied No supporters with an electrifying speech in Glasgow.

It came as the last poll of polls for whatscotlandthinks.org by Strathclyde University politics professor John Curtice showed the No camp leading the Yes camp by four points on 52-48, a widening of the gap by two points.

The final polls saw a YouGov Times/Sun survey of 3,237 voters put Better Together ahead of Yes Scotland by four percentage points at 52-48; a Survation/Daily Record poll showed the pro-Union group ahead by six points at 53-47.

An Ipsos/Mori survey for STV showed a 51-49 split in favour of Scotland remaining in the United Kingdom, and Panelbase's poll had the No camp in the lead by 52-48. All of the polls excluded undecided voters.

Mr Salmond told activists at Perth Concert Hall that today would be a day "which Scotland will never forget".

Hailing it as an opportunity of a ­lifetime, the SNP leader said the vote was a "precious chance" for nationalists "to leave our mark in the pages of history".

However, Better Together campaign director Blair McDougall warned: "No-one today can afford a protest vote."

He added: "If we vote to leave the UK there would be no going back, no matter the risks to our jobs, pensions and NHS."

Ahead of today's vote, counting officers in Scotland's 32 local council areas yesterday despatched ballot boxes to more than 2,600 polling stations across Scotland in time for them to open at 7am.

A record number of voters are ­registered. People who are registered to vote but unable to make it to their polling station today were reminded that emergency proxy votes could be arranged on the day.

Meanwhile, the Scottish Police ­Federation dismissed fears the poll could be hit by serious public disorder.

Activists from both campaigns will today mount major operations to get their vote out to the polls.

But after more than two years of constant debate and campaigning, the leading figures can only vote and wait like millions of ordinary Scots.

Mr Salmond will vote at Ritchie Hall in Strichen, while Deputy First Minister Nicola Sturgeon will cast her ballot at Broomhouse Community Hall in Glasgow.

Liberal Democrat Scottish Secretary Alistair Carmichael will vote at Evie Primary School in his Orkney constituency. Better Together leader Alistair Darling will vote in Edinburgh, while Gordon Brown will go to the polls in his Fife constituency.

All the leaders of the main UK parties, meanwhile, will be glued to their TVs. David Cameron, who is due to give a statement on Friday morning outside the famous No 10 door whatever the outcome, will be ensconced in Downing Street and will, according to a source, be "following events closely".

It is thought Ed Miliband will be the only UK party leader to watch the unfolding drama from Scotland as he is expected to be in Glasgow.

Nick Clegg, who yesterday raised the prospect Scots MPs could be barred from voting on some English-only ­legislation at Westminster as a result of handing further powers to Holyrood, is expected to watch the referendum from his home in Sheffield.

Leading figures and activists from the cross-party Better Together campaign will gather in the Marriott Hotel in Glasgow. The SNP will set up camp at Edinburgh's Our Dynamic Earth visitor attraction, overlooking Holyrood, as the results come in.

The first local result is expected at around 1.30am tomorrow, with North Lanarkshire favourite to declare first.

Results from Glasgow and ­Edinburgh are expected at around 5am when, despite the tight polls, the eventual outcome may become clear.

Scotland's chief counting officer Mary Pitcaithly hopes to announce the final result from the Royal Highland Centre in Ingliston, near Edinburgh, where voting figures will be compiled, by about 7am.

On a hectic final day of campaigning, Alex Salmond appealed directly to voters in an open letter, accusing the UK Government of generating daily "scare stories" and saying they had "no place in a sensible debate".

He added: "I ask only this. Make this decision with a clear head and a clear conscience. Know that by voting Yes what we take into our hands is a responsibility like no other - the responsibility to work together to make Scotland the nation it can be."

He began the day with a visit to a shopping centre in East Kilbride.

However, for the first time he tacitly acknowledged he could lose the vote, saying: "Whatever the result, this huge movement towards Yes is an outstanding feature of the campaign."

Last night 2,500 Yes supporters ­gathered in Glasgow's George Square, where they chanted and waved Saltires and heard speeches from socialist firebrand Tommy Sheridan and other pro-­independence campaigners.

Mr Brown electrified Better Together's final rally at a community hall in Maryhill, with onlookers praising his speech as the best of the campaign.

The former prime minister made an impassioned plea for Scots to vote No for the sake of their children and the country's future.

To rapturous applause from 600 supporters, many waving heart-shaped "Love Scotland, vote No" posters, he called on people to reclaim Scotland from the SNP and the Yes campaign.

He said: "Hold your heads high, show dignity and pride, be confident. Let's have confidence that our values are indeed the values of the majority of the people in Scotland. Have confidence, stand up and be counted tomorrow."

Meanwhile, both sides seized on figures showing a fall in unemployment and a record number of Scots in jobs.

Bookmakers said £10 million would be gambled on the outcome. William Hill said it had taken £2.5m in bets. They face paying out millions of pounds if the country votes Yes.