And we’re off! The Conservatives have moved the writ for the Brecon and Radnorshire by-election, having held off to ensure it is held on 1 August not 25 July. This means that, rather than the by-election taking place on the new prime minister’s first full day in office, the result will come through on his eighth.

It’s a risky move. Even in ideal circumstances for the governing party, if the Conservatives were perhaps six points ahead in the polls and the Liberal Democrats were bobbing along at the eight to ten per cent mark, we’d expect the Liberal Democrats to make a strong challenge in the seat, which they held from 1997 to 2015 and still hold in the Welsh Assembly.

And, of course, these are not ideal conditions for the Tories: the polls show that each of the parties is on around a quarter of the vote. Yet, for a variety of reasons, the Tory leadership election has been conducted almost entirely in reference to the Brexit Party, which, in both its Ukip and Brexit incarnations, has never won a seat from the Conservatives without the benefit of defection. This means there has been no real discussion about the electoral threat of the SNP or the Liberal Democrats, both of which have successfully won many, many seats from the Tory party and could do the same at the next election.

A visible reminder that there are other electoral threats out there – and the extreme likelihood that the Conservatives will have chosen a candidate who is near-perfectly optimised to increase those threats – may spoil the new leader’s honeymoon and weaken their leverage before parliament returns in the autumn for what could be a series of key votes.

Don’t forget that the Brexit Party won the European elections in the Powys local authority, where Brecon and Radnorshire is located, and the Liberal Democrats came second, just 4,000 votes behind. So, on paper, this seat, if the polls are about right, would be a tightly fought battle between the Liberal Democrats and the Brexit Party, even before you throw in the fact that the Conservative candidate, who is restanding, was found guilty of false accounting.

However, there are good reasons to believe it won’t be a straight fight between the Liberal Democrats and the Brexit Party: the latter showcased the same organisational weaknesses in Peterborough that were previously witnessed in Ukip and it would be a big surprise if the party demonstrated an ability to overcome them by the beginning of August. Added to its old institutional inability, that the new organisation has none of the data of the old means that it has even less idea where its voters are than Ukip did.

So it would be a shock if the Brexit Party could overcome those hurdles in a little over a month, in less favourable territory than Peterborough.

But the risk for the government, particularly if Boris Johnson is its leader, is that the Brexit Party can do well enough in Brecon and Radnorshire that the Conservatives finish third. The political gamble being made by the Tories is that, yes, Johnson will lose votes to the Liberal Democrats, but that he will make up the deficit by draining the air from the Brexit Party balloon.

So this by-election has the possibility to cause difficult questions for all of the three parties nominally in contention for the seat (Plaid Cymru and Labour have never really been a presence in this constituency). For the Liberal Democrats, it would be a worrying sign that their new voters were not well-geographically dispersed in their areas of previous strength. For the Brexit Party, it could underline the huge strides they have yet to take to win seats under first-past-the-post.

And for the Conservatives: it’s more likely than not that come the morning of 2 August, whichever frontbencher is sent out to defend Johnson, will be able to point out that they have, at least, neutered their Brexit Party problem. But what if they can’t?