Explainer-Scotland's leader Yousaf has resigned. What's next for SNP?

By Alistair Smout

LONDON (Reuters) - Scotland's leader Humza Yousaf resigned on Monday, further imperilling more than a decade of governance by the Scottish National Party (SNP) and setting back its aspirations of independence from Britain.

The crisis marks a stunning fall for the SNP and strengthens the hand of the UK opposition Labour Party ahead of a national election expected this year.

HOW DID THE SNP GET HERE?

The party achieved majority government in Scotland in 2011, leading to a 2014 independence referendum.

Though Scots voted 'No' to independence by 55% to 45%, the SNP consolidated 'Yes' supporters to win 56 of 59 Scottish seats in the UK parliament in 2015, making it Britain's third-biggest party, despite standing in fewer than a tenth of UK seats.

That domination has since lessened but remains a major hurdle to Labour's hopes of securing a majority at UK elections.

Under former leader Nicola Sturgeon, the SNP opposed Brexit at a 2016 referendum, a popular position in Scotland even though the UK as a whole voted to leave the EU.

The party has continued to push for a second referendum on independence from the UK.

In coalition with the Greens, the SNP has promoted environmental and social policies that alienated some traditionalists with its plans to relax rules for legal recognition of gender transitions.

Sturgeon resigned last year and has since become embroiled in a party funding scandal with her husband, who was charged this month with embezzling funds. Both deny wrongdoing.

When Yousaf replaced her, he was widely seen as a continuity candidate. But some SNP lawmakers have questioned the progressive priorities of the party under Sturgeon and Yousaf.

Last week, Yousaf said he would scrap the SNP's coalition with the Scottish Greens who were unhappy at his decision to toss out a key climate change target, aiming to govern instead as a minority. But he failed to garner the support needed to survive confidence votes due this week.

The Greens criticised Yousaf for yielding to "reactionary forces" in his party by abandoning the coalition agreement.

WHAT DO POLLING FOR ELECTIONS AND INDEPENDENCE SAY?

With the SNP's popularity sliding, a YouGov poll in April put Labour ahead of the SNP for a UK election for the first time since 2014.

A UK-wide general election must be held within the next nine months. If the SNP loses seats either in the Scottish or UK parliaments, it could undermine further the party's efforts to gain a mandate for a second independence referendum.

Opinion polls show a fairly static picture in appetite for independence, with the YouGov poll finding 53% of voters would reject independence and 47% would support it.

WHAT HAPPENS NOW?

Yousaf said he would stay on as interim first minister until a new SNP leader is chosen.

There are 28 days for a new first minister to be appointed, and the SNP will commence a fresh leadership contest in order to nominate someone to the position.

If no first minister commands the support of parliament after 28 days have passed, a new election to the Scottish parliament will be called.

(Reporting by Alistair Smout; Editing by Bernadette Baum)