NEARLY half the UK electorate is fearful of the SNP holding sway over the next government - but Labour voters are much more likely to embrace the prospect than Conservative supporters.

An exclusive poll for The Herald confirms the Conservatives' high profile campaign portraying Ed Miliband dancing to Alex Salmond's tune is striking a chord with large numbers of voters south of the Border.

However it also suggests SNP leader Nicola Sturgeon judged the public mood accurately when she used a major speech last weekend to send a "message of friendship and solidarity" to left-leaning voters down south.

Her pitch to traditional Labour voters elsewhere in the UK was designed to make it harder for Mr Miliband to turn his back on working with the Nationalists in the event of a hung parliament.

The SNP drew encouragement from the poll as Labour received a boost from a separate survey suggesting it has made up ground some ground on the Nationalists.

Ed Balls, the Shadow Chancellor, will today promise to "end Tory austerity" with his first Budget, as he campaigns in Scotland today.

Almost a third of Labour voters across the UK believe it would be good for the country if the SNP emerged with greater influence after May 7, compared with four out of 10 who said it would have a negative effect.

Overall, the poll by TNS, specially conducted for The Herald's Election 2015 supplement published today, shows 46 per cent of voters believe greater SNP influence would be negative and 22 per cent positive for the UK as whole. Some 32 per cent were unsure.

However, 29 per cent of Labour supporters felt it would be positive, compared with just 13 per cent of Conservatives.

According to the main TNS poll, which surveyed 1,197 voters between March 26 and 30, the Conservatives, on 33 per cent, enjoyed a slight lead over Labour on 32 per cent.

A separate ComRes/ITV News poll last night showed the SNP six points ahead of Labour in the 40 seats held by Ed Miliband and Jim Murphy's party before the election, a smaller lead than revealed by some previous surveys.

Support for the Nationalists was at 43 per cent, ahead of Labour on 37 per cent, the Tories on 13 per cent and the Lib Dems on two per cent, the same as UKIP and the Greens.

If the swing was repeated across Scotland, the SNP would win 30 seats to Labour's 27, with one apiece for the Lib Dems and Conservatives, according to the Scotland Votes website.

The main reasons people gave for voting SNP were because they wanted independence or felt Labour no longer represented them.

In a finding which illustrated the ongoing impact of the referendum, 56 per cent of voters said they were voting against the SNP "to keep Scotland part of the UK".

Asked what they would like to happen in a hung parliament with a significant number of SNP MPs' 41 per cent of battleground voters were opposed to the idea of the Nationalists entering a formal agreement with another party.

A similar total said the SNP should either go into coalition with Labour or prop up an Ed Miliband government through a looser arrangement.

The polls came as speculation about a possible post-election arrangement between the SNP and Labour continued to dominate the campaign in Scotland.

Ms Sturgeon yesterday said delaying a decision on renewing Britain's nuclear deterrent would be a "red line" issue for the SNP in any formal pact with Labour, a demand already ruled out by Ed Miliband.

However, her comments kept alive the possibility of the SNP supporting a minority Labour government on an issue by issue basis.

Nationalist hopes of winning concessions from Mr Miliband also received a boost when a group of left-wing Labour MPs warned they would not support his plan to reduce the deficit, in line with SNP calls to increase spending.

Both the SNP and Labour claimed their positions were vindicated after the Institute for Government think tank said that there were no barriers to a smaller party opening negotiations immediately after the election result but that as current Prime Minister David Cameron would get the first chance to propose a new coalition government to the Commons.

Commenting on The Herald's poll, SNP Westminster leader Angus Robertson said: "It shows substantial support among Labour voters across the UK for working with the SNP, which indicates that there is an appetite for the kind of progressive politics that Labour won't deliver if left to its own devices, such as reversing the cuts."

A Scottish Conservatives spokesman said: "It's clear that any people right across the UK, including in Scotland, are worried about an Ed Miliband government being held to ransom by the SNP.

"It would mean more borrowing, more debt, and most importantly, would weaken our United Kingdom."

Jim Murphy, the Scottish Labour leader, said of the ComRes/ITV News findings: "We are back in the fight but we are still the underdogs.

"If this poll is repeated on election day it could hand the keys to Downing Street back to David Cameron."

Lib Dem leader Nick Clegg, who will be campaigning in Scotland today, said: "There's always a danger that you get a bit of an unholy alliance between the Tories and the SNP, because the SNP want to talk up the threat of a Tory Britain and the Tories want to talk up the threat of an SNP Britain.

"So they are both very convenient bogeymen for each other."