Scotland's vote on independence this month means Queen Elizabeth faces a division in her kingdom not seen since the days of her namesake Elizabeth I at the start of the 17th century. But some things may not change so much.
Whatever the outcome, Queen Elizabeth is likely to still be Queen of Scotland, since most Scots are keen to retain her as head of state even if they vote to go it alone.
After almost 64 years on the throne, Elizabeth is set to overtake Queen Victoria in September next year as Britain's — and both England and Scotland's — longest reigning monarch. But celebrations then might be muted if Scots vote for independence this Sept. 18, although opinion polls suggest they will not.
The date of the potential split, March 24, 2016, is laden with historical significance: It would be exactly 413 years after the crowns of the two countries were united following the death of Elizabeth I in 1603.
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Should Scotland vote for independence, nationalists say Elizabeth, who is 88, would remain Queen of Scotland although they give no guarantee of the monarchy's long-term future.
"Scotland will be a constitutional monarchy for as long as the people of Scotland wish us to be so," the Scottish government, led by the Scottish Nationalist Party, says.
Although the Queen is assumed to back the union, under her constitutional role she must stay politically neutral.
Her only official comment on the referendum came in May in a message to the General Assembly of the Church of Scotland.
"In this important year of referendum, we pray that whatever the outcome, people of faith and people of good will, will work together for the social good of Scotland," she said.
However, she gave an indication of her views on a split of her realm during a speech to mark 25 years on the throne in 1977 when she referred to referendums on devolved governments in Scotland and Wales, which were later rejected by voters.
"I number Kings and Queens of England and of Scotland, and Princes of Wales among my ancestors and so I can readily understand these aspirations. But I cannot forget that I was crowned Queen of the United Kingdom of Great Britain and Northern Ireland."
Actions louder than words
Mary Macleod, a former policy adviser to the Queen and now a member of parliament, said the Queen's actions spoke louder than words.
"It will be something she will be looking at with extremely close interest because historically and to this day she feels Scotland is a very important part of the country as a whole," Macleod said.
Dickie Arbiter, the Queen's former press secretary, said Elizabeth had faced the same issue when Australians voted in 1999 against becoming a republic.
He said she took the view then it was for Australians to decide, and it would be the same for the Scots now.
"She's very pragmatic," Arbiter told Reuters.
Royal biographer Robert Lacey pointed out that Elizabeth was already head of state of 16 independent nations.
"I don't think that would be a problem for her at all. She's already Queen of Canada and Queen of Australia and Queen of New Zealand and queen of a dozen Commonwealth countries, quite independent of being Queen of Great Britain," he said.
Queen of Scots?
But amongst those campaigning for independence, there is also a feeling that not only should the union with England be ended, but also the Scottish monarchy.
Kenny MacAskill, Scotland's Justice Minister, has hinted an independent Scotland should hold a referendum on keeping the monarchy, and Dennis Canavan, the chairman of the Yes Scotland campaign, has said such a vote should take place quickly.
Polls have traditionally shown Scots are less enthusiastic about the royal family than the rest of Britain. However recent surveys suggest they would not want to ditch the sovereign.
A British Social Attitudes survey in June found that 62 per cent in Scotland thought an independent Scotland should keep the same king or queen as England.