If you believe the Conservatives - as a kind of thought experiment - Ed Miliband has been posted missing for the past few days.

Some coincidence, say those critics: Tony Blair puts in an appearance and his latest successor goes to ground.

Just for a change, you can see what the likes of Grant Shapps, Tory chairman, means by the jibe. What could Mr Miliband gain from juxtaposition to Labour's three-in-a-row winner? He might appear a little inadequate. Equally, how would it sound to much of the electorate if Ed was forced to say nice things about Tony? He might seem to be embracing a Blairite legacy they despise. So the leader hides - or, rather, campaigns in Bristol.

For Labour, it's a tricky little problem with large implications. It speaks to an unresolved ambivalence, not least on Mr Miliband's part. It reminds anyone who needs reminded that some in the party are still proud of Mr Blair. Others just wish he would disappear once and for all.

He's a hero and toxic simultaneously. He's the man, in one legend, who made Labour electable, who purged it of ideological fixations, who imposed a post-modern pragmatism and confounded the Tories. He is also the Iraq war criminal who has spent his political afterlife grubbing for wealth and hiring himself out to some of the seediest characters on the planet. Who would want to discuss that package "on the doorsteps"?

Clearly, it was no accident at all that Mr Blair chose Europe as his theme for a speech in his old Sedgefield constituency. Opposition to Conservative plans for a referendum on the UK's membership is one thing about which he and Mr Miliband can agree. These days, the "principled and intelligent case for Europe" causes only modest controversy in Labour's ranks. It was no great task, either, for the former leader to accept that inequality is the issue of the hour. Few say otherwise.

But even when Mr Blair tells his audience that Labour in Scotland has "a great new leader", the same question faces Jim Murphy as faces Mr Miliband: does that kind of praise help or hinder? Fans will remind you that Blairite Labour won big in Scotland between 1997 and 2005, even if its share of the vote dropped from 45.6 per cent - a distant dream today - to 39.5 per cent during those years. But did it win because it was Blairite, or just because aversion to the Tories had become so profound?

There are other ways to phrase the question. The referendum vote and every poll since have measured a spectacular collapse in Labour's Scottish support. There are explanations to suit almost every taste. "The Scots have all gone mad," say keening voices from the asylum. "The SNP is a cult," say gibbering followers of the Thatcher and Blair cults. Then, mercifully, there are people still able to stop and think.

The desire for independence continues. Labour's co-operation with the Tories before the vote sat ill. Voting for Mr Murphy's party has made no useful difference. The kind of historical process that did for the old Liberals is in train. And trust - faith, allegiance, a habit of belief - has gone. At this stage, the last explanation seems self-evident. The sense of having heard it all before from Labour has reduced the party in Scotland to the most desperate kind of negative campaigning.

Given that Mr Blair has been gone from government for almost eight years, his role in all of this might not be self-evident. It is no accident, though, that Mr Miliband was in Bristol rather than Sedgefield yesterday. It is no coincidence, equally, that his party, once utterly dominant in Scotland, has been reduced to fighting for its life in the aftermath of his leadership. He is emblematic, in the crudest shorthand, of what Labour became, or has become.

Did Mr Miliband's heart leap when he heard Mr Blair say: "I support him 100 per cent"? Perhaps it did. After all, the current leader's team has tried everything and the polls won't budge. You might guess, then, that someone advocated a touch of the old winning magic to heave Labour towards the finish line.

If so, it smacks of desperation. It also means that those around Mr Miliband have written off those places where Mr Blair's name earns contempt. The target for this campaign weapon can only be the sort of floating voters who helped to give Labour its landslide in 1997. Call them occasional Tories. Think of them as people liable to agree with Mr Blair about eurosceptic obsessions and flirtations with Ukip. Few Scottish constituencies will feature in the calculations.

It counts as a surrender, of a kind, by Mr Miliband. In his tentative way he has tried to banish Labour's Blairite past, either by confessing - in a general sort of way - that "mistakes" were made, or by refusing to talk about the ghosts of yesteryear. Now one notable ghost is all over the headlines again. Mr Miliband's earnest attempts to redefine the proper relationship between the state and capitalism have been reduced to a couple of questions for Mr Blair to bat aside.

In this, the leader's difficulty was obvious: he couldn't win. Had he refused the former Prime Minister's aid the Tories would have been all over the story. Yet by going along with the "intervention" he invites comparisons and earns the sort of endorsement that his candidates in Scotland and elsewhere could, let's say, do without.

It was Mr Miliband's call. Presumably he believes the votes he wants rest with people who don't think Mr Blair was so bad, in places Labour still believes it can win. If so, you can draw two conclusions. First, that the party hasn't really changed: Blairism is certainly not disowned. Secondly, the campaign is not going so well. Either Mr Miliband is happy to have his predecessor pitching in, or he has made a choice in extremis: "Whatever works".

Mr Murphy's devotion to Mr Blair is no secret. From the start, it was an odd (if minor) aspect to his elevation to the Scottish leadership. The very best you can say is that, entirely predictably, it hasn't helped. All those new-minted pledges on inequality and social justice don't obscure political lineages. Mr Blair once led his party to triumph in Scotland. That fact ceased to be relevant long ago. Here his endorsement of Mr Miliband is no sort of vote winner.

The leader did not feel able to refuse the gift: so much is obvious. Yesterday, amid all the polite reporting, few were reminding themselves that Mr Blair's reputation is these days a bit short of enviable. People know plenty: the fortunes earned, the Chilcot debacle, the dictators courted, and always the miserable war, its lies and diabolical consequences. To win "100 per cent" support from this character is no sort of prize.

It will be interesting, if not exactly elevating, to watch Labour's Scottish campaign throw the word "progressive" around beneath Mr Blair's dark shadow. In his day, he was the kind of politician his party wanted. Even now, that party does not repudiate him.