What's the thinking behind a second Scottish referendum bill?

The Scottish government has published its draft bill on a second independence referendum, but why now? Here, I attempt to answer some of the key questions being asked.

Does the new independence referendum bill commit the Scottish government to holding another vote?

No. It is a draft bill and the Scottish government is committed to consulting on it.

SNP ministers say they want to have the legislation ready in case they decide independence is the best, or only way, to protect Scotland's links with the EU.

What EU links do SNP ministers want to preserve?

Ideally, they would like Scotland - if not the whole of the UK - to remain in the EU.

At the very least they want Scotland - if not the whole of the UK - to remain in the European single market.

They are also seeking....

• further devolution of agriculture and fisheries powers

• a say on immigration

• and the ability to make some international agreements.

Why do they think Scotland should get a special deal on Brexit?

Because in Scotland, voters backed remain by 62% - 38% in the EU referendum, while the UK as a whole voted to leave.

The SNP's opponents insist it was a UK-wide decision and that it is the overall UK vote that matters.

Is a special deal possible?

In theory, yes. The Scottish government says it will publish detailed proposals in the coming weeks.

Its standing council on Europe has been looking at possible options.

Is a special deal for Scotland likely?

The UK government would need to agree to argue for one in its Brexit negotiations with the EU.

Conservative ministers don't seem keen but Theresa May has said she will consider suggestions from the devolved governments.

What happens if there is no special deal for Scotland?

This is the point when first minister, Nicola Sturgeon, will have to decide whether to go along with the UK's proposed terms for Brexit or to go for another independence vote.

Does Nicola Sturgeon have the power to call an independence referendum?

The first minister has made clear that she would seek the explicit legal authority for a vote from the UK government.

That's what happened in 2014. The power was lent to Holyrood under what's known as a section 30 order.

So, could the UK government block indyref2?

UK ministers could refuse to transfer the explicit powers for a referendum, yes.

Politically, that could backfire. My guess is that they would not want to risk driving up support for independence by obstructing a vote.

If the UK did try to block a referendum, could the Scottish government hold one anyway?

The SNP has previously argued that Holyrood could legislate for a non-binding, consultative referendum.

Critics think any attempt to do so would be rejected by the Scottish Parliament on legal advice because the constitution is specifically reserved to the UK parliament.

Does public opinion matter?

Of course. Having lost one referendum, Nicola Sturgeon cannot afford to lose another.

She is unlikely to call a vote that she is not very confident of winning.

What do the polls say?

They vary of course but broadly speaking they suggest support for independence is around the 45% recorded in the 2014 referendum.

There is not a trend that suggests there is a consistent majority for a "yes" vote.

The nationalists believe there could be a shift towards independence if Brexit looks like a bad deal for Scotland and if the UK government refuses to pursue a special deal.

What if there is no shift?

Big call for Nicola Sturgeon to make - whether to go for indyref2 or not.

Before Brexit it was widely thought the SNP would want to see 60% support for independence in polls over a six month period before deciding to call a vote.

Following the EU referendum, that no longer appears to be a crucial test.

There are those in the SNP urging caution. But others are convinced a referendum campaign would build the support required to win.

As I say, big call.

So, do you think there will be a Scottish independence referendum during the two year Brexit negotiation?

Honest answer is I don't know - sorry.

Nicola Sturgeon says it's "highly likely" if the UK government rejects her calls for Scotland to have special status.

At this stage, the threat or promise of another vote (depending on your point of view) is being used as a lever to try and secure such a deal.

If that doesn't work, Nicola Sturgeon will have to decide.

What I would say is that her exit strategy from the referendum route is not, at this stage, obvious.

And lastly, are the SNP ready to fight a referendum campaign?

Not quite. They need a new prospectus for independence that takes into account the changed circumstances Brexit brings.

It would need to address big questions - old and new - over issues such as low oil prices, EU relations, Scotland's currency, access to the UK single market and common travel area.

At least some of this is being considered by the party's economic growth commission, headed by former MSP Andrew Wilson.