The Scottish government has published draft legislation for a possible second referendum on Scottish independence.
It wants to hold a vote after the pandemic but "in the first half of the new parliamentary term". So does it mean indyref2 is now inevitable?
Hasn't Scotland already had an independence referendum?
Yes, in September 2014.
Scottish voters were given the choice of staying in the UK or becoming an independent country.
They backed staying the UK by 55% to 45%.
Why is it back in the spotlight now?
In one word - Brexit.
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 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.
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.
So far, 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.
A series of opinion polls suggesting that a majority of people in Scotland were now in favour of independence rattled unionists ahead of the Scottish Parliament election in May - although some more recent polls have suggested that support for remaining in the UK could have edged narrowly ahead again.
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.
Unionists say Ms Sturgeon and her government should be focusing on tackling Covid and 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 on how to secure another referendum.
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.
This may be partly why a draft bill has now been published, setting out how a referendum can be held once the Covid pandemic ends if the May elections produces another pro-independence majority at Holyrood.
The Scottish government has not given a specific date, but says it wants a referendum to be held in the first half of the next parliamentary term.
It says there can be "no democratic justification whatsoever" for Westminster to attempt to block it - but has not said what it will do if formal consent is not forthcoming.
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 appeared to have shifted over the past year, with more than 20 consecutive polls indicating majority support for independence.
However, polling expert Prof Sir John Curtice says support for the SNP and for independence is now consistently lower in the polls than it was at the beginning of the year.
He wrote last week that the past half dozen polls have averaged 51% for No and 49% for Yes once undecideds were removed.
This represents a five-point fall in support for independence compared with the position in the last half dozen polls conducted before the end of last year.
Sir John also said it was the first time that No have been ahead in a running average of the polls since this time last year.
Meanwhile, polls have also suggested that the SNP's hopes of winning a majority in this May's election are also on a knife edge.