The most telling moment in Labour's worst-ever election night came around 4am.

The defeated former Labour MP for Glasgow South West, Ian Davidson, declared that his leader Jim Murphy should "do the honourable thing" and resign forthwith.

"He wasted no time in sticking the knife" said one Labourite in the BBC's election night green room in Pacific Quay.

Mr Davidson had famously announced toward the end of the referendum campaign that all that remained for the Unionists was "to bayonet the wounded". But there was no need for the SNP to fix bayonets. Labour dead were littered across the polling stations of Scotland.

The SNP had won the most remarkable landslide in electoral history. Going from six seats to 56 in only five years is beyond astounding. The losers in the independence referendum eight months ago had got their own back on Labour - in spades.

As former First Minister, Alex Salmond pointed out, there hasn't been a swing like this since 1835. But since only about 40,000 people in Scotland had the vote back then, it was hardly a relevant comparison.

Certainly, nothing like this has ever happened in modern times. SNP swings of 34 per cent and 35 per cent are unprecedented in general elections.

The swing in Willie Bain's Glasgow North East - a seat the opinion pollsters had suggested might remain in Labour hands - reached 39.3 per cent and broke the BBCs swingometer.

The former SNP minister, Mike Russell, tweeted that this wasn't a "tsunami"; it was an "extinction level event". It certainly looked like the end of days for the Scottish Labour Party.

The Shadow Foreign Secretary, Douglas Alexander, was defeated by 20-year-old student Mhairi Black in Paisley, making her the youngest MP since 1667. She said she intended to finish her politics degree even though she was going to Westminster. One suspects she might pass.

Jim Murphy, the former Labour minister and current Scottish Labour leader, lost East Renfrewshire, the seat he had taken from the Tories back in 1997. Mr Murphy made a dignified speech, insisting that he would remain leader and that the fight-back would begin right here.

Under normal circumstances this would have been vainglorious nonsense. He is neither an MP nor an MSP and has presided over Labour's greatest ever defeat. But the problem for the Scottish Labour Party is that there is no one else to take over.

Other Labour casualties were less gracious. The former MP for Linlithgow, Michael Connarty, announced that the voters of Scotland had been "duped" by a "personality cult" supported by the "forces of darkness". The fightback ended there.

The only Labour MP left standing after the nightmare was Ian Murray in Edinburgh South. He carries an onerous responsibility as the sole representative of the Scottish Labour Party in Westminster. Since he has already stated his opposition to Trident and austerity he may be adopted as a mascot by the 56 Nationalist parliamentarians.

But even Mr Murray owed his victory in part to circumstance and Nicola Sturgeon. His opponent, the SNP candidate Ian Hay, had been outed as a so-called "cybernat" with the Twitter name "Paco McSheepie". Ms Sturgeon was not pleased and had hung the sheep out to dry by saying that "the voters would decide" his fate. They did.

They also decided the fate of the Scottish Liberal Democrats by defeating all but one of their MPs. This included UK political stars such as the Treasury Secretary, Danny Alexander in Inverness, and the former LibDem leader, Charles Kennedy, in Ross, Skye and Lochaber. He was the youngest MP in Westminster once, in 1983 when he was 23 years old.

The LibDems were defeated by significant margins. The days when northern Scotland was orange county appear to be over. The Last Liberal in Scotland is now Alistair Carmichael in Orkney and Shetland.

But the dogged hero of the night was the mild-mannered Conservative MP David Mundell, who scraped home in Dumfries saving the Tories from a 1997-style wipe out. In an election where the Conservatives had triumphed in the rest of the UK, this would have been more than a humiliation for David Cameron.

Mr Salmond may still jeer that there are more giant pandas in Scotland than Tory MPs. But Mr Mundell will be able to say there are now also more pandas than there are Labour MPs or Liberal Democrats.

The former First Minister was returned as expected as MP for Gordon, the seat long held by the Liberal Democrat veteran Malcolm Bruce. But Mr Salmond struck a curiously jarring note when he announced that "the Scottish lion has roared tonight".

Really, they don't say testosterone-freighted things like that in Nicola Sturgeon's female-friendly SNP. It sounded almost anti-English. Most of the victorious SNP MPs avoided crude triumphalism, probably because most of them could hardly believe that they had won.

The SNP may have led the opinion polls from day one in this campaign, but few of the candidates ever believed that they could win 56 seats out of 59. Indeed, I have difficulty believing it myself, and I counted them all in overnight. It is extremely hard to comprehend just how dramatic a change there has been in the Scottish political landscape.

It will be some time before we learn what it means for Scotland and the UK's constitutional future. Clearly, the Nationalists are not going to have quite the clout in Westminster that they might have expected on this showing. They will not hold the balance of power. The "nightmare on Downing Street", as the Conservative press called it, has been averted.

Scotland may have a stronger voice in Westminster, but it will not be calling the shots. The SNP may have won 56 seats, but that is still only 56 out of 650. It will be difficult to hold Westminster's feet to the fire if they are simply ignored.

My hunch, however, is that the sheer scale of the SNP victory in Scotland will have constitutional implications. The Smith reforms are dead and Scotland will surely acquire another round of devolution.

Scottish Question Time in the Commons is going to look rather interesting. It will be 57 MPs on the opposition benches against David Mundell (surely he must be rewarded with the Scottish Secretaryship) plus tumbleweed.

It may be that there is another independence referendum as soon as 2017 when the Conservatives hold their in/out referendum on the European Union, though the mechanism for this remains obscure.

The message for Westminster should be that the UK constitution itself is past its sell by date. It is surely time for that federal reconstruction of Britain, with an elected senate replacing the House of Lords.

There should be a constitutional convention in the UK to look at this and also replacing the first past the post electoral system. Though given the conservatism of the UK political establishment I wouldn't hold your breath.

What we can say is that this has been a remarkable generational shift in Scottish politics. The last party to win this number of votes was the old Scottish Unionist Party back in the 1950s when Scotland was Conservative country.

After Mrs Thatcher came along, Scotland abandoned the Tories and it was Labour that was winning more than 50 seats, finally eliminating the Conservatives altogether in 1997.

Now the SNP has all but wiped out Labour, and turned the map of Scotland Nationalist yellow. But it is the speed of this transformation that is so difficult to comprehend. The other shifts in voter alignment took place over decades; this has happened in only five years.

History is speeding up; and it may be that, five years from now, Scotland may no longer be part of the United Kingdom as we understand it