Scotland joined England in a political union in 1707. While Prime Minister Theresa May's centre-right Conservative Party has a majority in the UK Parliament, it has only one lawmaker in Scotland and 54 of the 59 Scottish seats are held by Scottish First Minister Nicola Sturgeon's Scottish National Party (SNP).

Legally, who decides?Britain's national Parliament is sovereign and is therefore the only legitimate authority to legislate on constitutional issues. Such matters are among the "reserved" topics that in general are not devolved to the Scottish Parliament.

With prior agreement between governments in London and Edinburgh, the UK Government can devolve power temporarily from Westminster to the Scottish Parliament, Holyrood, making a bill to legislate for an independence referendum in Edinburgh legally watertight. This is known as a Section 30 order.

This is what happened to allow the 2014 independence referendum.

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Many observers believe May's government ultimately will give its blessing to a secession vote once more if requested, to avoid being seen to stand in the way of the Scottish people.

A likely point of contention would be the timing of a new vote; the Scottish Government wants to keep the vote within the two-year time frame in which Britain leaves the European Union so Scotland has a chance of retaining its EU membership.

The UK Government will likely seek to push that timing back.

Could Scotland just call another vote on its own?Constitutional experts say that if the Scottish Parliament voted to hold another independence referendum without the consent of Westminster, the Scottish bill would be legally challenged, ultimately at the UK's highest judicial body, the Supreme Court.

The Scottish could still choose to press ahead with a symbolic, non-legally binding vote. However Scotland's independence referendum legislation, prepared in October in readiness for this potential outcome, tacitly recognises that the UK Government will have to sign off on allowing a vote, constitutional experts say. What they sayDefence Secretary Michael Fallon last month told Scotland's Herald newspaper that Scotland could "forget it" if it expected London to facilitate a new referendum on independence, causing a row with the Scottish Government who accused him of arrogance.

Michael Gove, another Conservative lawmaker, said a few days later that the decision on a new vote was down to the British Prime Minister and that Sturgeon would be "foolish" to try to call one.

After the Supreme Court in London ruled that the devolved assembly in Edinburgh did not need to be consulted on triggering Brexit, Sturgeon asked: "Is Scotland content for our future to be dictated by an increasingly right-wing Westminster Government with just one MP here? Or is it better that we take our future into our own hands?"