But, for those of us who are partial to a dram, we all know that evenings which end suffused in a warm glow exact a price later on. And those of us who especially like a malt, such as the delicate Speyside offering they call 'Glenrothes', know that moments of rich and rare enjoyment are no insurance against a sore head in due course. So how long will Gordon's Glenrothes Glow last?

Well, on the credit side, it appears he has significantly reduced one threat and it also seems he's marginalising another. The Salmond leap in the polls is over and the nationalist threat to sitting Labour MPs must be subsiding. Gordon Banks in Ochil, and others who feared a tartan surge, suddenly look as though they may live to fight for the Union another day.

As can those Labour MPs in the north of England who have Lib Dem opponents in second place. Nick Clegg's party saw its vote collapse and the performance in Glenrothes confirms the trend in the polls. A slice of soft Lib Dem support is returning to Labour. Possibly those who were alienated by Iraq now feel it is safe to come back.

The ebbing of support for both the SNP and the Lib Dems in Glenrothes reflects what other measures of public opinion have been saying. Both these parties are facing a more difficult period ahead – and each is likely to be the other's deadliest enemy in Scotland with battles in Argyll, Inverness and Gordon looming.

But, away from these absorbing contests, the battle for who will be the next Prime Minister is a return to a more traditional fight – a straightforward duel between Labour and Tory. And that isn't the only thing about the current political scene that looks more familiar and old-fashioned.

Watching the Labour Party over the last few weeks in the House of Commons, what has been striking is how deeply it has slipped back into its old comfort zone. And the same thing holds, even more powerfully, for the Prime Minister.

Taxpayer support for stricken banks has got Labour MPs talking about the virtues of nationalisation and the merits of Michael Foot's 1983 manifesto. Hints about Keynesian economics from the Chancellor have inspired the backbenches with visions of spending splurges and massive public works programmes.

It won't be long before Labour members harbour hopes that Gordon will commission a statue of Mick McGahey for Parliament Square and a reading of Hugh MacDiarmid's 'Hymn To Lenin' in place of prayers in the Commons.

This Seventies revival on the backbenches – what Hazel Blears has referred to in the past as "Life On Mars politics" – has also been matched by a trip back in time on the Prime Minister's part. One of the reasons why he has seemed happier in the past few weeks is that he has been reprising the role he used to enjoy. He has become his own Chancellor, flying round the globe to discuss IMF rescues with assorted sheikhs and potentates.

Like an actor slipping back into the repertory role with which he made his name, because the transfer to the West End went wrong, the PM is back trying to do what he was comfortable with before all the problems of his premiership overwhelmed him.

Now this turn of events may, like a glass or two of the best Speyside malts, cheer Labour spirits, but there is a cost. And Gordon knows it.

After all, it was he who expended such political capital in the 1990s ridding Labour of its reputation as a traditional left-wing tax, borrow and spend party. He argued that it was impossible to build the New Jerusalem on a mountain of debt. And he made a virtue of "prudence for a purpose". But with our deficit, even before the recession hits us full on, already ballooning and debt escalating yet further, the image of fiscal rectitude is smashed forever. You can't be Mick McGahey's heir and Margaret Thatcher's child at the same time.

And as well as having forsaken prudence, there's another virtue Gordon has abandoned. Change. When he became PM he promised that "the work of change" would begin. Now, 18 months later, Peter Mandelson and Alastair Campbell are back and Gordon is offering more, much more, of the same. Instead of cleaning up politics we've gone back to the old spin cycle.

Barack Obama's victory has underlined the power of the change message, and the polls show that just as many people here as in the States believe Britain is heading in the wrong direction.

But, if back to its traditions is where Gordon has chosen to take Labour, then perhaps it's in Labour's past we should look for the best guide to what happened on Thursday. And there is a striking parallel – in 1978.

That was the year Donald Dewar won the Garscadden by-election, seeing off a nationalist challenge just at the time the SNP were on the crest of an electoral wave. Labour held the seat, albeit with a reduced majority, and the Dewar victory was a prelude to a series of SNP reverses to come in the next year. It was also a prelude to something else which happened in 1979, when a country which had seen through nationalism saw that economic bad times meant we needed a change of direction at the very top.

Gordon is entitled to enjoy his vintage Glenrothes moment, but for those who know their Labour history the taste of this victory can't help but inspire some very sobering thoughts.