There are two very different elements to polling of the conservative leadership race: polling of Conservative party members – used for predicting who is going to win, and polling of the general public, which is generally being used to argue about the electoral appeal of the different candidates.

Let’s take members polling first. The only professionally conducted polls of party members are done by YouGov, with the most recent conducted last month just before May’s resignation. It found Boris Johnson was the first choice for members on 39%. More importantly the poll asked party members to rank candidates in order of preference, allowing YouGov to work out head to head figures for each potential pair of candidates. Suffice to say, Boris Johnson won them all. The closest pairing was Johnson vs Raab on 59%-41% though given these two are both appealing to the brexiteer elements of the parliamentary Tory party that seems an unlikely run off. The more plausible contests of Johnson v Gove, Johnson v Hunt or Johnson v Javid would all be clear victories for Johnson. In the event Johnson does not get through, Dominic Raab also beats the remaining candidates, though by less convincing margins. As things stood in May, whichever of the leading “hard Brexit” candidates, Johnson or Raab, reached the final two would win.

It is worth remembering that data is from back in May, so it is possible that opinion has changed already. Certainly there is still time for opinion to change in the future. The only other data we have on party members is from ConservativeHome’s surveys of their mailing list of party members. I think they last did paired run-offs in April, but they’ve asked about members’ preferred leader more recently and found Johnson retaining a strong lead.

Perhaps more open to interpretation are the polls of the general public, especially since they are often used to make the case for various candidates in terms of their electoral appeal. Polls about leadership candidates are often very much exercises in name recognition – the fact is that many of the people being asked about are relatively obscure figures who most people who are not political anoraks know little about. If you ask the public whether Mark Harper would make a good or bad Prime Minister then the overwhelming majority of people obviously say they don’t know who Mark Harper is (most of those who do answer the question are Labour and Lib Dem supporters giving negative answers, presumably on the basis that they feel any Tory would be a bad Prime Minister!)

Any attempt to gauge public attitudes towards the candidates needs to be viewed through this prism. Here, for example, are the most recent YouGov figures on if people will make good or bad Prime Minister. Boris Johnson is one of the best known politicians in the country, so has the highest proportion thinking he will make a good Prime Minister (26%). However, he also has the highest proportion thinking he would be a bad Prime Minister (53%). Michael Gove and Jeremy Hunt are also familiar to most people, though both have proportionately more negative ratings than Johnson (Gove 15% good, 51% bad; Hunt 15% good, 46% bad). After that recognition falls away – 55% of people gave an opinion about Sajid Javid (18% good, 37% bad), 42% Dominic Raab (14% good, 28% bad) and so on.

Some have used this to argue the lesser known candidates are more popular candidates on the basis of their net figures, or the proportion of those who know who they are who give them a positive rating. For example, in the YouGov poll of those who expressed an opinion about Rory Stewart over 40% were positive… but that’s because over 70% of people didn’t have an opinion. There is no guarantee that the opinions of the 29% who did are a reflection of what the rest of the country might think were they to form an opinion of him (though in their defence, it may be easier to start with a blank slate and convert people who have no opinion than change the views of those who have already formed negative perceptions of the better known candidates). On the subject of Rory Stewart, it should be noted that he is the only candidate who has really improved his ratings substantially during the campaign, albeit from an almost non-existent base. In May 5% thought he would make a good PM, by last week that had risen to 12%. On the other hand, the criticism that he is the candidate popular amongst people who aren’t Conservative does seem to have some truth to it – his best ratings are amongst Labour and Liberal Democrat voters.

That brings us more directly to the issue of the electoral impact; which candidate would do better at winning over voters at a general election? I should begin by adding a caveat here – people are not necessarily good judges of these matters. They may have an idea of whether they like Boris Johnson or Michael Gove, but they don’t know the policies they are campaigning on, how the media are reporting them, whether the party has united behind them and so on. We are asking people to imagine a hypothetical situation when they really don’t have much to go on. In cases where people don’t even know much about the candidates themselves, like Matt Hancock or Rory Stewart, I don’t think there’s any real point in even asking the polling question. Respondents simply don’t know enough to judge.

For the better known candidates, it can at least tell us something and, when it is asked, there is a clear pattern. This YouGov poll for Lord Bell found the Conservative party on 29% under Boris Johnson, 24% under Dominic Raab, 21% under Hunt, 20% under Gove and 22% under Javid. Johnson clearly does better – but it appears to be a straight forward transfer of support directly from the Brexit party, who drop to 13%. There is a similar but smaller effect from Dominic Raab becoming leader. The fairly obvious interpretation is that the impact we’re seeing here is not Johnson or Raab’s magnetic personalities, but Brexit party voters returning to the Conservative party if the the new leader is someone they trust to deliver a genuine Brexit. That’s certainly something I would expect to happen… but it does also mean that such support would likely be conditional upon the new leader actually delivering Brexit in a timely fashion (and, one assumes, since it would be happening on their watch, delivering a Brexit in a way that isn’t a total disaster).

My advice for people looking for polling clues to future Tory performance under different leaders is that the impact of the candidates’ personalities may in reality be dwarfed by the impact of whether or not they actually deliver something that their potential voters perceive as a successful Brexit.