The exit poll suggests vindication for Ms Sturgeon and a disaster for the other parties in Scotland, all of which were dragged down by their UK leaders.

The First Minister put a second independence referendum at the heart of her campaign, saying a vote for her party was not just a chance to “escape Brexit”, but that she would interpret it as a “clear instruction” for holding Indyref in 2020.

Although Ms Sturgeon dialled down the independence message in the closing days, urging people to vote SNP tactically mainly to lock Mr Johnson out of power, the unambiguous text of her manifesto will allow her to claim a mandate for that new vote on the constitution.

READ MORE: Scotland Decides: Exit poll predicts Conservative majority as polls close 

The poll’s prediction of a thumping Tory majority south of the border and the near certainty that Brexit will now go ahead, can only add fuel to those demands.

The constitutional crisis is likely to be one of the first thing’s in Mr Johnson’s in-tray.

The generic referendum legislation which would pave the way for Indyref2 is due to complete its passage through Holyrood next Thursday.

Ms Sturgeon has also said she will request the transfer of power to hold the referendum, under Section 30 of the 1998 Scotland Act, before Christmas.

The Prime Minister has said he will simply mark it “return to sender”, but to dismiss it out of hand would be to invite a further backlash and boost support for independence.

However even if Mr Johnson attempts to let the SNP leader down gently, the issue is now certain to dominate the next Scottish Parliament election in 2021.

If the poll is correct, and the SNP have achieved a second tsunami in a general election, there is a very real chance that the party will do likewise at Holyrood, repeating the absolute majority of 2011.

Even Scottish Secretary Alister Jack and former Scottish Tory Ruth Davidson have said a win on that scale would constitute a “democratic mandate” for another referendum.

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The First Minister last night urged caution in response to the poll.

She said on Twitter it suggested a “good night” for the SNP, but added: “it is just an exit poll and there are many marginals, so let’s just wait and see. What it indicates UK wide though is grim.”

The exit poll also suggested the profound failure of the Scottish Tory campaign, which was almost exclusively focused on attacking Ms Sturgeon and on Indyref2.

Both proved considerably more popular than what the Tories were offering - Boris and Brexit.

In a country where Mr Johnson’s popularity rating is abysmal and almost two-thirds of people voted to Remain in the EU, the Tories were always going to struggle.

But they convinced themselves they had found a way to avoid a wipe-out of their 13 MPs, and talked up their chances of winning In Lanark & Hamilton East and Central Ayrshire.  

Ms Davidson even promised this week that she would swim naked in Loch Ness if the SNP won more than 50 seats.

“I will happily wager to strip naked on the banks of Loch Ness and subject myself to a Hogmanay wild swimming session should such a result occur, safe in the knowledge that my modesty (and others' eyeballs) will remain unmolested," she wrote. 

Both she and Nessie appear set for a shock.

Scottish Labour, too, had hopes of holding on to many of their seven MPs, and possibly regaining some of their former heartland seats in Glasgow and North Lanarkshire. 

However the party suffered because of Jeremy Corbyn, who was not seen as a credible candidate for Prime Minister, and because the SNP offered an alternative which was equally opposed to Mr Johnson, clear in its opposition to Brexit, and stood up for Scotland.

READ MORE: General election 2019: When will Scotland's results be announced? 

In Richard Leonard, Scottish Labour also has a leader who, while he improved over the campaign, remains an inconspicuous, lacklustre figure after more than two years in the job.  

Having led Scottish Labour to a fifth-place rout in May’s European election, his position must now be in doubt.

Willie Rennie must also be considering if this was his last election after eight years as Scottish Liberal Democrat leader and whether it is time for a new face for 2021.

HeraldScotland:

His party had four MPs in 2017, including the rock-solid seat of Orkney & Shetland. 

But it was the East Dunbartonshire incumbent, Jo Swinson, who really mattered, alienating voters with a manifesto pledge to stop Brexit without another referendum, and patronising nonsense about her being the next Prime Minister.

The LibDems also had a chance to overturn the smallest majority in the UK - the two votes of the SNP’s Stephen Gethins in North East Fife.

If they have failed - and this is Mr Rennie’s patch at Holyrood as well - it will be humiliating.