For decades the dominant force in Scottish politics, the Labour brand is now putting off Scots voters, according to a new poll.

Support for the party's key election pledge fell when voters were told it was a Scottish Labour policy.

Scots are also divided over whether leaving the European Union should trigger another independence referendum, the poll found.

The finding comes just a day after Nicola Sturgeon confirmed that an EU exit against the will of Scots could lead to another vote.

Dr Michael Turner, research director at BMG Research, who carried out the poll for The Herald, said: “The results are clear; in Scotland, it would seem, the Labour party brand is toxic.”

On the EU, he added, "the headline figures suggest that Scots are split on whether a second independence referendum should be triggered".

Despite the bad news for Labour, the poll shows the party in second place ahead of Ruth Davidson's Scottish Conservatives, with the SNP maintaining its clear lead.

In the constituency vote the findings put the SNP on 43 per cent, Scottish Labour 17 per cent, the Scottish Conservatives 13 per cent, and the Liberal Democrats 5 per cent.

In the second regional list vote the SNP was on 37 per cent, Labour 16 per cent, the Conservatives 13 per cent, the Greens 6 per cent, Liberal Democrats 5 per cent and Ukip 3 per cent.

However, nearly one in five voters said that they were still undecided with less than three weeks to go until polling day.

As well as how they would vote those surveyed were asked about Scottish Labour's flagship proposal for a 1p rise in income tax to be spent on protecting education and other services.

The findings suggest that the policy is quite popular, with support outweighing opposition 51 per cent to 21 per cent.

There was less backing for the plan, however, when voters were told it was a Scottish Labour proposal.

Support dropped by more than eight percentage points when Scottish Labour was mentioned.

The biggest falls were among SNP and Conservative supporters, although there was a rise among Labour supporters, as might be expected.

However, among undecided voters support dropped by around five percentage points when Labour's name was attached to the policy.

The poll also found 55 per cent of Scots want to remain in the EU compared to 35 per cent who back leaving.

Almost three in four Labour supporters, 72%, say they will vote to stay in the EU compared to just over half, 56 per cent, of SNP supporters and 46 per cent of Scottish Conservatives.

Asked whether a second independence referendum should be triggered if Scotland was taken out of the EU against the will of Scottish voters, 43 per cent were in favour and 45 per cent against.

The results also show that younger Scots are overwhelmingly in favour of a second vote, with older voters strongly opposed.

Yesterday the First Minister confirmed that the SNP's manifesto would not include a pledge to hold another independence vote in the next parliament.

The SNP leader said that she believed that there should be another referendum only when most Scots agreed - or there was a significant change in circumstances, such as a 'Brexit' opposed by most Scots.

Dr Turner said that the Labour findings “should be deeply concerning for a party that is looking to make-up ground since its shattering electoral defeat at the last General Election.

"If Conservative, SNP and undecided voters are all less likely to trust ideas put forward by Labour, even if they like Labour ideas, then where is left for the party in Scotland?”

On the EU findings he said there was a "very strong generational divide to these results.

"Interestingly, poverty and deprivation also appear to play a key role.

"Those living in more affluent areas are least in favour of a second referendum, whereas those living in Scotland’s most deprived areas strongly support a second referendum being triggered."

The findings came as former Prime Minister Tony Blair played down the role of referendums.

Asked about the upcoming EU membership vote he said: “Everyone always says ‘you’ve got to listen to the people’. When you listen to the people, you hear different things.”

BMG Research surveyed 1,013 Scots between April 11 and 15.

A Scottish Labour spokesman said: "This election is about how we use the new powers of the Scottish Parliament to stop the cuts and invest in public services. People were promised the referendum was a once in a generation vote and the SNP should stick to that promise. Instead of rerunning the arguments of the past every party should focus on the future.

"This poll confirms strong support for Kezia Dugdale's plan for fairer taxes, including a 50p top rate of tax for the richest 1 per cent, to stop the cuts and invest in education. Faced with the choice between using the powers of the Scottish Parliament to invest in our economy or carrying on with the SNP's cuts, Labour will use the powers."

A spokesman for the SNP said: ''This is another very encouraging poll for the SNP, and we will step up our campaign right across Scotland this week as we launch our manifesto.

"We take nothing for granted and will work hard for every vote - and the only way people can be sure of re-electing Nicola Sturgeon as First Minister leading a Government in a position to deliver our manifesto is to give both votes to the SNP."

On another independence referendum Liberal Democrat leader Willie Rennie said: “The last thing Scotland needs is a First Minister who will spend the next five years campaigning for independence and pouring over the runes to decide what constitutes a change in circumstances while public services decline.”

Meanwhile, a separate poll by Panelbase for the Sunday Times put Labour and the Scottish Conservatives neck and neck in the race for second place.