Scotland’s voters will not be deterred from independence by bullying and intimidation from the UK government or big business, first minister Alex Salmond has declared amid intense campaigning across the nation ahead of Thursday’s referendum.

Mr Salmond rejected comments from a former deputy leader of his Scottish National party, who said that oil major BP and banks “in cahoots with an English Tory prime minister” would face a “day of reckoning” after independence.

Campaigning has reached a fever pitch as a flurry of polls released on Saturday suggested the vote remained too close to call.

“The day after a Yes vote will be a day of celebration for the people, not reckoning for big companies drawn into the No campaign by Downing Street,” Mr Salmond said. “We will approach the success of Yes with magnanimity to all.”

Pro-union politicians had seized on the claim from Jim Sillars, a leftwing deputy leader of the SNP until the early 1990s but since then a fierce critic of the party’s leadership, that BP could face nationalisation after a Yes vote.

Mr Salmond, who shared a campaign platform with Mr Sillars this week, said his long-time rival had merely been expressing widely shared anger at the role of David Cameron, UK prime minister, in mustering businesses to oppose independence.

The “underhand Tory tactics” were backfiring, Mr Salmond said. “[Voters] are in no mood to be bullied by big Westminster government putting pressure on big business to intimidate the people of Scotland.”

Mr Cameron has led an effort to orchestrate companies to intervene in the referendum, evoking the war against Hitler in a rousing "call to arms" to more than 100 business leaders in Downing Street last Monday.

Pro-union activists took comfort on Saturday from a poll commissioned by the Better Together campaign against independence that found support for a No vote at 54 per cent compared with 46 per cent for Yes, when undecided voters were excluded.

"The nearer it gets, a lot of the undecided voters have looked into the precipice and they've stepped back,” said Jim Murphy, Labour member of the UK parliament.

A survey for the Observer by Opinium, its first of the referendum campaign, also found the pro-union campaign enjoying a six-point lead, with 53 per cent supporting No and 47 per cent for Yes when undecideds are excluded.

Yes activists were cheered by a sharply contrasting internet-based poll by ICM for the Sunday Telegraph that put Yes in the lead by 54 per cent to 46 per cent for No, when “don’t knows” are stripped out.

In a poll for the Sunday Times, Panelbase put No at 51 per cent and Yes at 49, a one point swing to Yes since the companies’ previous survey a week ago.

The Yes lead was first reported by ICM, but John Curtice, Scotland’s highest profile psephologist, said the result came with a “substantial health warning” given its smaller than usual sample size of just 705 respondents.

A telephone poll by ICM for the Guardian that was released on Friday put the No camp in the lead by a razor-thin two points.

Scotland has been gripped in recent days by increasingly passionate and sometimes highly testy debate on the risks and opportunities of leaving the UK.

The Yes Scotland campaign said that on Saturday it expected to muster 35,000 volunteers at 473 registered street stalls, with 2.6m leaflets to be delivered in 48 hours. No campaigners were also active on street corners across Scotland.

In the biggest rally to be organised by opponents of independence since the campaign began, thousands of Protestant unionists from across Scotland, Northern Ireland and the rest of the UK marched through Edinburgh in support of remaining in the UK.

The mainstream No campaign disassociated itself from the march, organised by the Grand Orange Lodge of Scotland, for fear of being associated with sectarian tensions between Protestant and Catholic communities.

Gordon Brown, former UK prime minister, told a Labour gathering in Kirkcaldy that Scots should embrace a “patriotic vision for the future” that did not involve independence. “We are proud that we share and co-operate as part of the United Kingdom,” Mr Brown said.

Politics trumped shopping in the centre of Glasgow on Saturday afternoon as hundreds of campaigners from both sides lined the city’s busiest thoroughfares.

“In one city (Edinburgh), you’ve got a very divisive, aggressive march,” said Aileen McKay, a 21-year-old stage manager. “Just a few miles away (in Glasgow) we’re asking people what their hopes and dreams are.”

Hundreds of cards were dangling from a string she had tied between two trees on Sauchiehall Street.

“Hope my wee mammy is watching us win from heaven,” read one. Others were more blunt. “No Tories,” said the one next to it.