The chart above shows the results of some fascinating new polling which YouGov has kindly shared with ConservativeHome at the outset of the final, month-long round in the leadership election.

Up-front, it shows that Boris Johnson is expected by voters to bring some additional electoral advantage over Jeremy Hunt, though not to a vast degree. Instead, as Marcus Roberts notes for our panel, the far more powerful determinant of voting intention is the question of whether the Conservative Party fulfils its promise to carry out Brexit and take this country out of the European Union.

You might think this is obvious, but bear in mind that the outgoing Prime Minister, at least, seemed to think that a failure to keep such a promise was an electorally viable thing to do and the need for such polling becomes clear.

The Brexit Party stands to lose a majority of its vote share when Brexit happens – again something which you might imagine to be obvious (the clue’s in the name, after all) but which apparently is not so clear to those warning that the Conservatives cannot and should not “try to out-Brexit the Brexit Party” in response to Farage’s resurrection. On the contrary, it seems that the only answer to the phenomenon is to out-Brexit them, perhaps not in campaigning style or rhetorical purity but through the key distinguishing factor available to the Conservatives and not to their new rivals: being in Parliament and being in (at least some degree of) power.

In practice, I suspect this poll might even understate the degree to which fulfilling Brexit will determine a future election. YouGov finds that in the hypothetical scenario of a post-Brexit election with Boris Johnson as leader, nine per cent of people still intend to vote Brexit Party. This might be an expression of current scepticism that this would happen, or that it would be done properly. It might be a genuine reflection of an intention to continue backing Farage against the so-called legacy parties. But it assumes that the Brexit Party in its current bullish form, with its current platform, would still exist. At minimum I’d suggest there would be opportunities to squeeze that vote down hard in such a scenario.

What also interesting is that while these findings suggest that getting Brexit done would help the Conservative Party to address its Brexit Party problem, the same does not help Labour address its Lib Dem problem. Crucially, neither would delaying Brexit further – in both scenarios, Labour stay just about neck and neck with the yellow peril, which is a grim prospect for the Opposition. Perhaps, Labour Remainers would counter, that could change by becoming an openly Remainer party, but we simply don’t know if that’s the case. As it stands, neither leaving nor staying shows Labour reassert itself.

There’s one final point to note, which is about the specific terms of the question YouGov have put. “Imagine that a General Election is held in Spring next year…” That does matter, and will play into the ponderings of various people around the Tory leadership candidates. This timing would mean that the second scenario – in which “Brexit has not yet happened” – is an election in which either Prime Minister Johnson or Prime Minister Hunt has conceded yet another delay, of six months or more after 31st October, in effect continuing in the vein of Theresa May’s failure.

I do wonder if there would be any differences to these results if you were to test opinion on an election before 31st October, with Brexit yet to happen but hingeing on the outcome – a not-impossible event. Evidently a huge amount would depend on whether the new Conservative leader could convince Brexit Party supporters they could be trusted to get the job done – and in attempting that task they would be contending with the toxicity of May’s legacy and the sometimes mercurial whims of Nigel Farage. I’d be surprised if that wasn’t already being tested in private.