image captionIndependence campaigners have been hoping for a new referendum since 2014
Boris Johnson is due to visit Scotland on Thursday, when he is expected to argue that the country is better off as part of the United Kingdom.
The trip is widely seen as being part of a “charm offensive” by the prime minister in response to rising support for Scottish independence.
What is the Scottish independence debate about?
Put simply, it’s the question of whether Scotland should remain part of the UK or become an independent country.
Hasn’t Scotland already had an independence referendum?
Yes, with Scottish voters backing staying in the UK by 55% to 45% back in September 2014.
Why is it back in the spotlight now?
The independence debate never really went away, but Scotland’s first minister Nicola Sturgeon started openly pushing for another referendum - often referred to as indyref2 - immediately after the UK voted to leave the EU in 2016.
Scottish voters backed Remain in the EU referendum by 62% to 38%, but the UK as a whole voted to Leave by 52% to 48%.
For nationalists, this was proof that Scotland needed to take its future into its own hands rather than being tied to the UK and its Conservative government.
image captionThe SNP’s plan is for an independent Scotland to rejoin the EU as quickly as possible
Many wanted indyref2 to be held before the UK left the EU in a bid to stop Scotland being “dragged out against its will” - but the argument is now that independence could allow Scotland to rejoin the EU in the future.
The SNP, which forms a pro-independence majority at Holyrood alongside the Scottish Greens, has spent much of the past five years arguing that its electoral success alongside the Brexit vote means it has a “cast-iron mandate” to hold a referendum.
It has so far failed to deliver indyref2 because the UK government has refused to grant the formal consent that Ms Sturgeon has previously said would be needed to ensure any referendum is seen as being legal.
But a series of opinion polls suggesting that more people in Scotland now favour independence has rattled unionists ahead of the Scottish Parliament election in May - when the SNP looks to be on course for another victory.
Is there going to be another referendum?
Not surprisingly, opponents of independence - including the prime minister - don’t want another vote on the issue.
They argue that the 2014 referendum was, in Ms Sturgeon’s own words at the time, a once in a generation opportunity - which Mr Johnson has suggested should mean another one should not be held for about 40 years.
image captionMr Johnson has suggested that another referendum should not be held for decades
Unionists say Ms Sturgeon and her government should be focusing on recovering from the Covid pandemic and on improving public services like health and education rather than independence.
They also say that rejoining the EU would not be a straightforward process for an independent Scotland - and could potentially lead to a hard border between Scotland and England.
And they accuse the SNP of failing to give clear answers to key questions over issues such as currency.
So what is Ms Sturgeon’s plan?
There have been divisions in the SNP over its strategy for securing another referendum in the face of this opposition.
Ms Sturgeon has predicted that the UK government’s hardline stance will crumble if there is another pro-independence majority in the Scottish Parliament after May.
But some MPs and grassroots independence supporters are not convinced that this will happen and have accused Ms Sturgeon and the SNP hierarchy of being too cautious in their approach.
image captionMany Scottish voters believe Ms Sturgeon has handled the Covid pandemic better than Mr Johnson
Perhaps partly in a bid to placate some of those dissenting voices, the SNP published an 11-point “roadmap to a referendum” last week, alongside a newly-formed “independence taskforce”.
The roadmap says an SNP government will legislate for a referendum to be held once the Covid pandemic ends if there is a pro-independence majority in the Scottish Parliament after May’s election.
It says the party will “vigorously oppose” any legal challenge to this plan from the UK government - but also stresses that a referendum would only go ahead if it was deemed to be legal.
Would Scots actually vote for independence?
Opinion polls, excluding don’t knows, had previously suggested a narrow majority of Scots want to remain in the UK - but things appear to have shifted quite significantly over the past year, with 20 consecutive polls indicating majority support for independence.
Polling expert Prof Sir John Curtice says that support for independence has consistently averaged 54% since last summer, which he says suggests that it “may have been a step change in the balance of public opinion rather than a continually growing movement in favour of Yes.”
Sir John also says that it is the view of many people that Ms Sturgeon has handled the pandemic better than Mr Johnson. This may have caused some former No voters to change their minds and support independence
And with the polls suggesting the SNP is on currently on course to win an overall majority in the Scottish Parliament elections in May. Sir John says that the country “seems headed for a significant clash between the UK and Scottish governments over whether another independence referendum should be held”.