For centuries the Union Jack has been the symbol of British power across the globe but a bid by secessionists in Scotland to break the union with England has thrust the future of the red-white-and-blue flag into question.
Gracing gunboats, guitars and even iPhones, the Union Flag has by turns served as a banner of imperial might and of British identity for everyone from monarchs to the Sex Pistols.
But Scotland's white-on-blue diagonal St Andrew's cross could be cut out of the flag if Scots vote to leave the United Kingdom in a referendum on Sept. 18.
As the Union Flag has not been adopted as Britain's official flag, even the prospect of independence has unfurled a quandary for admirers as no one has full authority over the flag.
"This situation is terribly British in that we are almost unique among developed nations in muddling through," said Charles Ashburner, chief executive of the London-based Flag Institute, a charity that studies and documents flags.
"Virtually every other country has this sorted out, with legislation for the flag and its use, and this needs to change for the UK if Scotland votes for or against independence."
With three overlapping crosses, the flag merges the English red-on-white cross of St George, Scotland's St Andrew's cross and Ireland's red-on-white diagonal cross of St Patrick.
The red dragon of Wales is not included in the flag, which traces its history to 1606 when King James VI of Scotland joined the flags of Scotland and England.
For admirers, the Union Flag is an expression of patriotism for the United Kingdom and the calling card of a lucrative industry selling popular British culture to the world.
But for opponents, the flag symbolises an archaic British jingoism that helped an English-led 'warrior nation' occupy a far-flung empire and dominate the Welsh, Scots and Irish.
So powerful is its symbolism that riots erupted in Northern Ireland last year after nationalist politicians voted to remove the flag from Belfast city hall on all but 17 days of the year.
A KINGDOM UNITED?
Above the Scottish parliament, the St Andrew's Saltire has central position flanked by the European Union flag, a ring of 12 golden stars against azure, and the Union Flag.
But even the idea of breaking the union could unravel the Union Flag into some of its parts, which are used by national supporters at the soccer World Cup or the Six Nations rugby union championship.
"It's a union flag, so if there's no union we don't need it any more," Josie Alderton, an English resident of Carlisle in northern England near the Scottish border, told Reuters.
"Each of the nations, England, Scotland, Ireland and Wales, have their own flags, why would we need to keep this one?"
When asked what would happen to the Union Jack if Scotland voted for independence, a spokesman for Prime Minister David Cameron declined to speculate, saying the government was focused on making the case for the United Kingdom to stay together.
Change could have consequences far beyond Britain: it features on the flags of more than 20 countries including Australia and New Zealand as well as on the flag of the U.S. state of Hawaii, Barack Obama's birthplace.
An earlier version of Union flag even featured on the first flag to have any resemblance to the current Stars and Stripes of the United States, though Britain's colours were later dropped.
New Zealand has signalled it may drop the Union Jack from its flag, following Canada, South Africa and Hong Kong.
But for the keepers of Britain's traditions, changing the flag is a step too far.
"We're in favour of keeping the status quo and personally I'm of the view that if things are working, leave them alone," said Thomas Woodcock, the boss - or Garter King of Arms - at the 530-year-old College of Arms, which oversees matters relating to heraldry.
"We don't want the flag to become overly politicised and we don't need to rush into anything."