While Boris Johnson's Conservative Party swept the opposition aside across much of England on his promise to "get Brexit done", Scottish and Irish nationalists made record gains at the UK general election.

In Scotland, the Scottish National Party (SNP) captured 48 of the 59 parliamentary seats, setting the scene for a second independence vote.

Meanwhile, Northern Ireland elected more Irish nationalists to Britain's parliament than pro-British unionists, a first since the partition in 1921. The nationalists' victory in the province prompted fresh calls for a so-called "border poll".

Could Boris Johnson's victory, by giving him a clear mandate for Brexit, spell the disintegration of the UK?

Euronews looks at the implications of the general election results for the union that has bound England, Wales, Scotland and Northern Ireland for centuries.

The 'Brexit problem'

Both Scotland and Northern Ireland voted in large numbers to remain in the EU in the 2016 referendum - unlike most of England.

Scotland voted by 62% to remain in the EU, Northern Ireland 56%.

As noted by Nicola McEwen, Professor of Territorial Politics at the University Edingburgh, the EU has played an important role in keeping the four-nation union together.

"Devolution was introduced to Scotland, Wales and Northern Ireland in 1999 within the context of EU membership. EU laws and regulations may have helped to contain institutional divergences, as well as providing a supranational, post-sovereign framework within which multiple territorial identities could coexist," McEwen wrote in a publication.

"Brexit risks destabilising the delicate balance between political autonomy and national unity brought about by devolution," the expert warned.

'Painful nationalist standoff'

Jim Gallagher, a research fellow at Nuffield College, Oxford and visiting Professor of Government at Glasgow University, told Euronews that while Johnson's victory did not mean the end of the union, it presented an "unprecedented challenge" to it.

And the reason is that English, Scottish and Irish nationalism seems set for a clash.

Nicola Sturgeon said the SNP's performance in the election was a clear mandate for a second referendum on Scottish independence.

Scotland, England's political partner for 300 years, voted against splitting from the United Kingdom by 55% to 45% in 2014.

But Scots backed staying in the European Union in the 2016 referendum and Sturgeon argues Brexit means they should have another say on independence.

READ MORE: UK PM tells Sturgeon he's against a second Scottish independence vote

"England clearly voted for Brexit. Boris Johnson can claim two mandates for Brexit. The 2016 referendum’s narrow majority, and this week’s election victory in which he won a majority of the seats, but with under 45% of the vote," Gallagher said.

"Scotland voted for neither Brexit nor Boris and the Scottish National Party will say that the only way to avoid both is independence.

"But the SNP’s Nicola Sturgeon lost an independence referendum in 2014 with 45% of the vote, and though won nearly all Scotland’s Westminster seats it too was with 45% of the vote in 2019," he continued.

"There will be a very painful stand-off between these two nationalist parties -- Boris the British or English Nationalist, and Nicola the Scottish," the academic warned.

"But Boris holds the key to any future independence referendum and will not accept that 45% of Scottish votes for the SNP require him to open that door."

In a telephone call on Friday, Johnson indeed told Sturgeon he was opposed to another vote.

"The Prime Minister made clear how he remained opposed to a second independence referendum, standing with the majority of people in Scotland who do not want to return to division and uncertainty," Johnson's office said in a statement. "He added how the result of the 2014 referendum was decisive and should be respected."

Sturgeon immediately hit back on Twitter.

Votes loom with uncertain outcomes

In Northern Ireland, nationalists also said the result paved the way towards a vote on whether there should be a united Ireland.

"We are heading towards a border poll, I can't give you a definitive date, but we need to do the spadework now and prepare ourselves," Sinn Fein leader Mary Lou McDonald said.

"We need to, in an orderly fashion, structure the conversation about a new Ireland and constitutional change. I don't think unionism should be alarmed or frightened, this is a huge opportunity for everybody who lives on this island."

READ MORE: Nationalists win big in Northern Ireland, prompting calls for border poll

Unionists say they were betrayed by Johnson's Brexit deal with Brussels which, according to them, would create an economic border between Britain and Northern Ireland.

But throughout the election campaign, Johnson said he was committed to the union and denied accusations that his Brexit deal would create an economic barrier between the British mainland and Northern Ireland.

"The Irish question is one of unification or not, rather than independence, and it requires the assent of the Republic of Ireland after a referendum there too," Gallagher told Euronews.

"Holding one (“a border poll”, as it is called) is a decision for the UK government, though there is a legal test for when one should be held, unlike Scotland," he said.

The expert told Euronews that both in the Scottish and Irish cases, "the result is unpredictable but inevitably narrow: and that is the problem. Neither would unite the country".

"The big lesson of the UK’s Brexit referendum is not just that a new EU relationship is difficult, but that referendum on emotional, existential issues divide rather than unite countries."

Avenues for compromise?

According to Gallagher, only mutual concessions may help avoid a breakup of the union.

"In the end, the only stable solution is one of compromise, in which people with different aspirations in Scotland and Northern Ireland each get some of what they want, rather than one side or the other being a winner take all," Gallagher told Euronews.

One possible avenue for compromise includes allocating more powers to the devolved administrations of Scotland and Northern Ireland -- particularly as Brexit implies that what were once EU competencies will be returned to Britain.

Solving the Irish border issue in a way that's acceptable for Dublin, Belfast and Brussels will be key as well.

"Johnson’s challenge will be to find a way in each case to accommodate Scottish or Northern Ireland aspirations while retaining the essential structure of the UK."

"His scope to do that will depend to some degree on the deal he eventually does with the EU. It will be a bumpy ride, and it is likely that the Scottish problem will be the first in his intray," Gallagher said.

READ MORE: Europe reacts: Time frame for post-Brexit trade deal 'is challenging', says EU chief