If Scotland votes Yes to independence it would prompt a crisis for Northern Ireland unionists and could spark political instability, an expert has said.
Generations of migration between the two countries have created close cultural and historical links. In places, the gap between the two coasts is hardly 20 miles.
Loyalists fly the Scottish saltire every summer during their pro-British marching season celebrating the 1690 victory of William of Orange over Catholic King James II during the Battle of the Boyne.
Professor Peter Shirlow is an academic specialising in conflict resolution at Queen's University Belfast (QUB) and said a Yes vote next month would be a shock to the whole body politic of the UK.
"It would be a point of instability, it would be a sense that we are moving in one direction, which is the break up of the UK, that would lead at some point to unification (with the Republic of Ireland).
"Sinn Fein would be energised by that, which would add more to fractures we have in Northern Ireland.
"We have a political institution which is not evolving, going from one crisis to the next. A Yes vote would most certainly be a crisis for unionism."
In the 1600s the Plantation of Ulster by English and Scots settlers created large swathes of largely pro-union Protestants in Northern Ireland, mainly but not exclusively concentrated in the eastern half of the country.
In the 1800s many Irish Catholics moved the other way due to industrialisation in Britain and famine at home. Belfast merchants had close economic ties with their counterparts across the Irish Sea.
Contemporary migrants are more likely to be students from Northern Ireland heading to Scottish universities. Large numbers of football fans regularly cross the water to watch Glasgow Rangers or Celtic.
Street violence in recent years has highlighted political and religious differences surrounding identity which still exist between unionist and nationalist communities in Northern Ireland.
Since the 1998 Good Friday peace agreement that ended IRA and loyalist violence, a devolved powersharing administration has been established at Stormont. Sinn Fein and the Democratic Unionists are the two largest parties.
Recently Sinn Fein president Gerry Adams said the political institutions faced their greatest crisis since 1998. Stormont F irst Minister Peter Robinson responded by warning that an impasse over welfare reform was the most likely issue to force a collapse of the five-party ministerial executive.
Professor Shirlow said both sides would be affected by a Scottish Yes vote.
"A Yes vote would be a shock to the whole body politic of the UK. Anything which is constitutional would be felt quite strongly here.
"Out of the four countries that make up the UK, it would be an issue here. This is not something that is on everyone's lips but if the vote goes Yes it might be."
Dr David Hume, director of services at the Grand Orange Lodge of Ireland, has noted thousands of the organisation's members will participate in a Scottish Orange Order march in Edinburgh shortly before the referendum.
He said: "We want Scotland to remain with us as part of the United Kingdom because we believe we have a better future together that way.
"We hope that the campaign for an independent Scotland does not succeed. We hope the people of Scotland say no to the proposal.
"The Union would be the poorer if Scotland were to leave the Union, and Scotland would be the poorer."
Earlier this year DUP MP Ian Paisley Jnr said a Yes vote would drive a wedge between people in Northern Ireland and encourage republicanism.
Sinn Fein Deputy First Minister Martin McGuinness has also warned it is an issue which could be used to create divisions in the powersharing government.
He told Stormont's assembly: " I think all of us should resist the temptation to be drawn into something that will be decided elsewhere."
After 30 years of sectarian conflict, Northern Ireland has cemented a peace process which saw gunmen lay down arms and former sworn enemies enter into government together.
Yet disagreement over issues such as controversial parades, Irish or British flags and dealing with the toxic legacy of troubles deaths has polarised some within the two communities.
Both will be watching as Scotland decides.