EIGHTEEN months ago, when the opinion polls gave No a 20-point lead or more, yesterday's referendum result would have seemed an unlikely disappointment for the Better Together campaign.

When it finally became clear Scots had voted to stay in the UK by the decisive if not overwhelming margin of 10 percentage points, there were sighs of relief at the Glasgow hotel where Alistair Darling's team had set up their through-the-night base. The campaign had survived a genuine threat of defeat in the precarious days after a grenade of a poll from YouGov on September 7 put Yes ahead by 51 per cent to 49 per cent.

It emerged with a result clear enough and, with a turnout of 85 per cent, comprehensive enough to settle the question of independence for years to come.

A number of things saved the day for Better Together.

As the pound slumped and shares in major Scots firms nosedived, banks and business leaders spoke out to reinforce warnings about an independent Scotland's economic prospects.

The No camp also began to tackle head on the SNP's claim that Scotland's devolved NHS was under threat from privatisation and spending cuts down south, a vote grabbing argument it had complacently ignored for weeks as too flimsy to take seriously.

No's efforts were helped when Alex Salmond blundered badly at the critical moment. Behind the wheel of a bandwagon he needed to persuade people to jump on board, to join his winning side, travel with him and make history. Instead he took his eyes off the road, picking an unnecessary fight with the BBC that produced only damaging images of a mass protest outside the corporation's Clydeside HQ.

More important than any of those factors, though, was a joint promise by the three main UK parties to agree on a fresh package of devolved powers for Holyrood. If it looked like a panicked response that's because it was. But it succeeded in convincing voters that the parties would act, according to a clear timetable, rather than squabble half-heartedly about their three conflicting plans before hoofing them into the long grass.

What no-one could have predicted when Johann Lamont, Ruth Davidson and Willie Rennie made their pledge during a hastily arranged and generally excruciating press conference overlooking the Scottish Parliament is that it would set in train a potentially seismic constitutional shake-up of the whole UK.

The past few days have seen what Jim Murphy called an "English awakening". The prospect of greater autonomy for Scotland produced a stirring of discontent in the Tory shires and a determination to secure more powers in Labour's northern cities.

In his statement on the steps of Downing Street yesterday, David Cameron promised to address both.

It was his proposal to introduce "English votes for laws" at Westminster that came as a surprise; a nasty shock, in fact, from Labour's point of view.

The idea that English MPs alone should vote on English only issues at Westminster was included in the last Conservative manifesto as an answer to the West Lothian Question. It could severely undermine a future Labour government which lacked a majority in England to pass legislation on health, education or a host of other issues. Labour's Douglas Alexander described the move as a "knee-jerk reaction driven more by politics than by a considered judgment of the needs of the constitution".

But whether Mr Cameron is able to satisfy the demands of his backbenchers and clip the wings of Scots MPs remains to be seen. His timetable matches the fast-track process for devolving more powers to Holyrood, which means legislation will be drafted but not passed before next May's election. An incoming Labour government could tear up the plans but Mr Cameron's gambit raises the prospect of a bruising election campaign in which the Tories and Ukip compete over who stands up for England.

So much for Labour and the Tories being in bed together. Mr Salmond's supposed "Better Together alliance" was over precisely 90 minutes before the final referendum result was officially declared. With the finely-balanced UK election just eight months away, normal service has been resumed between the old enemies.