SCOTTISH voters have so far been solidly immune to the Ukip phenomenon, never electing as much as a councillor or giving the party the 5% vote share it needed to hold its deposit in recent parliamentary ­by-elections.

But that may owe more to the country's electoral landscape than in-built hostility.

Last week, a Survation poll found a majority of people in Scotland supported the policies of Nigel Farage's party to curb immigration, cut overseas aid and crack down on benefits claimants.

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However, while disenchanted voters south of the Border can go to Ukip, in Scotland the SNP is the master of taking support from other parties.

Nor does Ukip's "anti-politics" message - that Labour, the Conservatives and Liberal Democrats are as awful as each other - resonate as strongly in Scotland, where the SNP remains remarkably popular.

And it is hard to imagine how England-first Ukip could ever really prosper beyond England.

Yet Ukip's journey from fringe of the fringe to centre stage means its loser status in Scotland cannot be taken as read.

In recent years its performance in Scotland has been partially handicapped by destructive in-fighting between an old guard led by former Scottish leader Lord Monckton, and a new top team sponsored by Farage and party HQ.

Farage's men are now in place, and the European elections saw a slick rollout of election material and billboard posters in Scotland.

Constant media coverage of Farage and attacks by other parties also ensured every voter had heard of Ukip, giving it a brand recognition out of all proportion to its powerbase.

Many of those interviewed this weekend about why they had voted for the party said it was because the party talked their language, and said the things about immigration they felt. So in that regard, Ukip also maintained a distinctive sales pitch north of the Border.

The party picked up 155 council seats in England on Thursday with around 17% of the vote, down on the 23% of last year's county elections because of a poor showing in London.

Tonight it is expected to be first in both MEP numbers and UK vote share in the European elections. In Scotland, the odds are probably against it - it needs to double its 5.2% vote share of 2009 for a seat. However, the SNP needs three times Ukip's vote to keep them out and win a third MEP.

Both are big asks, and the outcome is hard to predict, especially with Ukip's publicity blaze.

Whatever happens, pollster Professor John Curtice has said it is "utterly misleading" to infer the Scottish independence referendum result from the European elections - the result of the latter means little for the former.

But if David Coburn is elected as an MEP for Ukip, it would introduce a wild card to the campaign. Unionist parties, despite their fear and confusion over Ukip, will claim that a pro-Union Ukip MEP in Scotland signals that the SNP is on the slide, and that, having snubbed Alex Salmond's appeal to reject Ukip, Scots voters will stick two fingers up to the First Minister in September.

Coburn will also have a bully pulpit to spread Ukip's particular twist on the referendum.

Immigration is the dog that has yet to bark in the independence campaign.

Salmond's White Paper offers ammunition to the Unionist parties by advocating looser controls and "healthy population growth" through inward migration after a Yes vote, but so far they have been reluctant to use it, although privately the Better Together campaign admits it will push the issue if the poll results narrow.

Having Ukip talk about immigration instead would be extremely useful for the parties, letting them stand back and avoid accusations of low politics, but also watching the issue go for a test drive.

If voters appeared more likely to reject independence because of immigration, then the other parties would feel on safer ground to focus on the subject themselves.

Even if Coburn loses tonight and there is a Yes vote in September, Ukip could still be hugely important here because the party's success in England would surely colour the independence negotiations with Westminster.

In 2012, Farage told the Sunday Herald that people in the rest of the UK would never agree to Scotland getting a "fat cheque" on its way out the Union, and Alex Salmond was "remarkably naive" to think otherwise.

He said: "Can you imagine the reaction from the English electorate? While the political class might want to pat Alex Salmond on the back, there's absolutely no way that the people of Wales, England and Northern Ireland would be happy with that, of course they wouldn't.

"And to think that they might just ignore it is daft. It's naive in the extreme."

Back then, Farage's warning seemed largely theoretical, but it now looks quite pertinent.

Ukip is in a position to set the tone for any independence negotiations because other parties are afraid of it and keen to follow its lead.

If Ukip says negotiations over the currency, the share of the national debate, the division of assets and keeping Trident ought to be as tough as possible to extract maximum advantage for the rest of the UK, the other parties will fall in line - because while Ukip is in the ascendent, a fight with Farage will feel like a fight with voters.

If Ukip fails to follow through on this week's successes at the general election, or if Farage is its sole MP, the other parties will relax, but by then hard bargaining over a Scottish exit from the UK would be the order of the day.

Never slow to interpret events to his liking, the First Minister will be able to claim success for Ukip is all the more reason to vote Yes, with only independence offering salvation from a future Ukip-Tory axis at Westminster.

But if that argument works and he gets his win in September, the aftermath could well be horrendously messy for the same reason.