Just fancy that. Jeremy Corbyn, according to a new poll by GfK for Business Insider, “is now a bigger vote-winner than Tony Blair”.

It isn’t exactly soothing reading for the left – some 53 per cent of voters say they would not consider voting for a Corbyn-led Labour Party versus 31 per cent who would. But Jez apparently thumps Tony in the electability stakes. 61 per cent would not consider voting Labour should Blair – somehow – have another shot at the leadership. A mere 23 per cent would.

The gulf between those two net scores – minus 22 per cent for Corbyn and minus 38 per cent for Blair – does indeed tell a story. Unfortunately, it isn’t quite the story the wilfully obtuse headline is telling. A poll like this might tell us something were it not already rendered so utterly and self-evidently redundant by its own premise.

Here’s the problem. Tony Blair hasn’t been the leader of the Labour Party for a decade. Even if his much-trailed and as yet unrealised “return to frontline politics” manifests itself as something more substantial than appearing on Marr a bit more often, he isn’t going to be leader of the Labour Party ever again. He has said – repeatedly and explicitly – that he knows this cannot happen.

Why? Because Tony Blair, tainted by the legacy of Iraq and by the disappointments of his ten years in office, is a deeply unpopular man. There are many indices against which we can measure Corbyn’s electability – or lack thereof – but “Tony Blair’s current popularity” is neither a fair nor illuminating one. As Iain Austin once said of a 2008 Times poll that asked voters whether they would prefer a beleaguered Gordon Brown or a younger, more charismatic leader: “There’s a ridiculous question. It’s like saying ‘do you want burnt toast or something nicer?’”

Of course, there’s nothing wrong in principle with comparing two politicians of varying shades of unpopularity. It’s true and provable that Corbyn is more popular than the Blair many Britons now think of as a snake oil salesman. But the poll’s exuberant conclusion – that Corbyn is “a bigger vote-winner than Tony Blair” – is complete bunkum.

A more sensible though still not all that useful comparison would compare the net favourability of Corbyn now and Blair in the weeks before 1 May 1997.

There are no prizes for guessing which of the two would end up lauded as the bigger vote winner then, but even then, it isn’t a like for like comparison. Think about it: for insight on where the Tories should go next you’d compare Theresa May with, say, Amber Rudd, not Thatcher or Douglas-Home.

Even if Blair won three general elections and Corbyn, on current evidence, will win none, whether the former was ever a bigger vote winner than the latter is missing the point. Comparing Corbyn with Bad Tony The War Criminal sets an unduly low bar for the current leadership. Blair’s continued unpopularity does present some structural challenges for the Labour Party of 2017, but marginally surpassing rock bottom isn’t success, nor is it evidence that you’re a vote winner par excellence.

And though there is evidence that Corbyn is winning some votes that escaped the Labour leaders who went before him – such as non-voters – the real problem is that too many Labour supporters are drawn to another “vote-winner”. Her name is Theresa May.