Prime Minister John Key has joked there will be a "small technical issue with our flag" should the UK break up in the wake of the Brexit vote.
Scotland's First Minister Nicola Sturgeon says it is "highly likely" there will be a repeat of 2014's independence referendum, because 62 percent of Scots voted to stay in the European Union (EU) las week -- across the UK, the result was 52-48 percent in favour of leaving.
She says many Scots voted to remain a part of the United Kingdom in 2014 so they could stay in the EU, and it's "democratically unacceptable" to now be dragged out against their will.
Meanwhile in Ireland, there are calls for a vote on unifying the island -- currently Northern Ireland is a part of the UK, while the rest is its own country, with no plans to quit the EU.
Like Scotland, Northern Ireland voted to remain in the EU, 56-44 percent.
The Great Britain flag, before Northern Ireland's stripes were added
The Union Jack flag, which was adopted in 1801, is made up of the individual English, Scottish and Irish flags -- the Irish bit being the diagonal red stripes. The former Great Britain flag didn't have these stripes.
The Union Jack adorns a number of flags belonging to former British colonies, including New Zealand's. Mr Key recently backed a controversial referendum to change the flag, which ended with voters sticking with the old flag.
But speculation the UK could split has Mr Key wondering if we might need to rethink our decision.
"What happens if Scotland goes and everybody else goes? Just putting it out there, you know," he told Paul Henry on Monday morning.
"The Union Jack won't be a union anymore, and it won't be a flag, then there's a small technical issue with our flag."