David Cameron will today make a last-ditch trip north to urge Scots to vote No in the referendum and keep the UK together.

The Prime Minister, who campaigned in Edinburgh last week, will be back in Scotland ahead of Thursday's crucial vote, which could lead to the break-up of the UK if there is a majority for independence.

With just three days of campaigning left, political leaders on both sides of the debate will be intensifying their efforts in a last-gasp attempt to win over undecided voters.

First Minister Alex Salmond will be meeting business leaders - including Brian Souter of Stagecoach and former William Hill chief executive Ralph Topping - in a bid to highlight the economic opportunities a Yes vote on Thursday could bring.

It comes in the wake of warnings from business and financial chiefs about the impact independence could have, with stores such as John Lewis and Asda last week suggesting prices could have to rise, while Deutsche Bank likened a vote to leave the UK to the mistakes which led to the Great Depression of the 1930s.

When Mr Cameron addressed financial services workers last week he told them it would break his heart if Scots voted Yes and split apart the UK "family of nations".

Today, however, he is expected to issue a stark warning towards waverers that there could be "no going back" if they opt for independence.

With polls continuing to suggest that the battle between the rival Yes and No camps is on a knife edge, Mr Salmond has said Thursday's referendum could be a "once in a lifetime opportunity" for people in Scotland.

Three polls that were published yesterday put the No campaign ahead - with a survey by Panelbase giving them a lead of just over one point when undecided voters are excluded. The survey, for the Sunday Times, put support for No at 50.6%, narrowly ahead of Yes on 49.4%.

A rival ICM poll recorded an eight-point lead for the pro-independence campaign - but experts urged caution because of its smaller than normal sample size.

Mr Salmond said yesterday that the Yes campaign was aiming to win a "substantial majority" in Thursday's referendum.

He told the BBC: "We're not aiming to win by one vote, we're aiming to achieve a substantial majority if we can."

The SNP leader went on to describe the referendum vote as a "once in a generation opportunity for Scotland".

When asked if he would pledge not to stage another such vote if the majority of Scots vote No to independence, the First Minister said: "My view is this is a once in a generation, perhaps even a once in a lifetime, opportunity for Scotland."

His deputy, Nicola Sturgeon, will also be out on the campaign trail this morning, alongside former Labour MP Dennis Canavan - now the chairman of the Yes Scotland campaign - and former Labour Lord Provost of Glasgow, Alex Mosson.

Meanwhile, two Liberal Democrat members of Mr Cameron's coalition Cabinet will be urging Scots to vote No, with both Scottish Secretary Alistair Carmichael and Chief Secretary to the Treasury Danny Alexander stressing the promises of more powers that are on offer from the pro-UK parties.