Is Alex Salmond more dangerous than the IRA?

Would Northern Ireland "end up like West Pakistan" if Scotland says "yes" in September? Could Scottish independence presage a return to the Troubles? These are just some of the concerns being voiced by Unionist leaders in Northern Ireland ahead of the upcoming referendum.

Protestants in Ulster have long celebrated their links with Scotland, so the prospect of Scotland leaving the Union has provoked a bout of soul-searching for some across the Irish Sea.

Earlier this month, Ian Paisley junior, Democratic Unionist MP for North Antrim, said that Scottish independence would embolden dissident Irish republicans, leading to violence on the streets of Northern Ireland.

Previously, former Ulster Unionist Party leader, Reg Empey, had said that if Scotland voted for independence, Northern Ireland would "end up like West Pakistan", with "a foreign country on one side of us and a foreign country on the other side of us".

In 2012, Tom Elliot, Lord Empey's successor as party leader, described the SNP as "a greater threat to the Union than the violence of the IRA".

Although the Good Friday Agreement guarantees that Northern Ireland's constitutional status can only be changed by a majority vote in the province, some Unionists are deeply concerned that the success of Scottish nationalism could see a clamour for a "border poll" on Irish unification.

Mike Nesbitt, current leader of the Ulster Unionist party, told The Sunday Herald: "For unionism having seen off Irish republicanism after half a century there is a fear of being undone by Scottish nationalism in the 21st century."

Nesbitt rejects the suggestion that Scottish independence could lead to a return to violence in Northern Ireland, but says that September's referendum, regardless of the result, will "politically recalibrate the United Kingdom". He added: "Even if Scotland says no to independence there is bound to be this push towards devo max and that will obviously have implications for Northern Ireland. Even Unionists whose political inclination is parity recognise that there economic arguments for breaking parity in areas such as corporation tax and air passenger duty."

But many Unionists are wary of any change to the status quo. The Democratic Unionist Party is the largest party in the devolved Stormont administration, but a significant minority of Protestants remains deeply opposed to power-sharing with Sinn Fein republicans.

Protestants are no longer an absolute majority in Northern Ireland, according to census figures released at the end of 2012. The flag protests that broke out over the removal of the Union flag from City Hall around the same time, and ongoing disturbances around Orange Order parades, have contributed to a siege mentality in loyalist communities and an existential crisis within Unionism itself.

"Unionists don't know who the hell they are and it's part of their ongoing dilemma," says Alex Kane, a columnist for the Belfast Telegraph and a leading unionist commentator in the city.

Former Northern Irish first minister and the architect of the Good Friday deal, Lord David Trimble, believes that Scottish independence could re-open the constitutional question in Northern Ireland. "If there was a Yes vote a lot of people would have to sit up and think and that opens up something," Trimble told the Sunday Herald.

"(Irish) republicans would get excited and say, 'It can be done'. Then there is a question, does their getting excited cause a problem? 'Probably' is the answer to that."

Trimble says, however, that the vast majority of Unionists in Northern Ireland are confident that there will be a 'no' vote in Scotland.

"Alex Salmond's main hope for success has always been to rile the English; to get the English riled and to use that to say to the Scots, 'Look, they hate you, they want rid of you'. It's a deeply cynical ploy but it has been obvious," the former Ulster Unionist Party leader said.

Wary of negative headlines in Scotland and the religious dynamic, Irish republicans have been reticent on the question of September's referendum. But former Sinn Fein director of publicity, Danny Morrison, says independence would have "a psychological effect" on Ulster Unionists.

"The majority Protestant community in the north is Presbyterian, not Anglican, and they identify their roots with dissenters from Scotland," he says. "Their forebears would be leaving the Union that they hold so dear in the north of Ireland."

But Morrison does not believe Scottish independence would be a game-changer in Northern Ireland. "Obviously, as an Irish republican I do express a little bit of schadenfreude at them all being upset at the old Union being broken up but does it bring Irish unity closer? No it doesn't."

Kane agrees, but for very different reasons, saying: "Sinn Fein have tried to play this bogeyman. 'When the Scots go, you're next', but they don't understand that a lot of nationalists - with a soft 'n' - are going to say, we don't want (unification), that's only going to cause far more problems than it's worth."

Although ahead in the polls, the No camp in Scotland has been accused of failing to articulate a positive vision of Unionism. Nesbitt says that the independence referendum should be seen as opportunity to "redefine in a more modern way what the union means".

"We have to redefine ourselves. Look at the 2012 Olympics, where you have a guy born in Somalia, whose religion is Muslim, whose forename is Mohamed, who very joyfully wraps himself in the Union flag," says Nesbitt. "That's a very different thing from what we called Britishness in 1914."

But James Mitchell, professor of politics at Edinburgh university, warns that attempts to create a pan-UK Unionist identity are fraught with danger. "Unionisms [across the UK] are very different," he says. "There are clearly common parts to these Unionisms but there are also differences. Any attempt to forge a common Unionism across the UK will fail, it can't happen."

He rejects the idea that independence would lead to a significant change in the relationship between Scotland and Northern Ireland, with which it has had strong cultural links for hundreds of years. "The key relationships are personal, social, family - and I don't think these need be disrupted at all," Mitchell says. There is a referendum on the horizon that Northern Irish leaders should be worried about, he says, but it is not the one in Scotland.

"The European aspect is far more important than the Scottish referendum. If Scotland voted for independence and stayed in the EU and the rest of the UK was then to vote to withdraw from Europe that would put Northern Ireland in a very difficult position," he says.

"You'd have the south [of Ireland] within the EU and Scotland within the EU. That is the most frightening thing from Northern Ireland's point of view."