The title assumes the Tories aren’t stupid enough to choose a Remain partisan for Prime Minister.
That’s a mighty big assumption considering they were not only fool enough to install the hapless Theresa May in the first place, but were fool enough to endure three excruciating years with her at the helm before, at last, pulling her off life support.
But let’s entertain the hypothetical in the title anyway.
Suppose they have just barely enough presence of mind to select a Prime Minister in favor of Leave.
What, then, are the best options for Farage?
In such a case, Farage can make the best use of his Brexit Party by wielding it as a hostage-taking-device to pressure the new Tory Prime Minister into advancing a Leave policy at the negotiations; or, failing diplomacy, into a no-deal exit.
From there, Farage himself would act as a shadow Prime Minister holding the threat of electoral oblivion over the head of the official Prime Minister.
Ideally, the government would go on to complete exiting the European Union in a way satisfactory to Farage, if for no higher reason than the Tory Party’s existence depends on it.
But there is an additional complication.
That complication is the recent threat by Remain Tories to vote no confidence in the government if a no-deal exit becomes likely.
Taking down a Tory government early would not be in Farage’s interest. It would be better to give sufficient time to observe how much the threat of the Brexit Party incentivizes the government to implement Leave policy as the October 31 deadline nears.
But if Remain Tories vote down the government, they would short-circuit Leave negotiations that Farage would hold significant indirect leverage over.
To scare them away from voting no confidence too soon, Farage should declare that the Brexit Party will either not stand for a general election, or, form an electoral pact with the Tories if it the election is initiated only by Remain Tories sabotaging an exit plan.
This deterrent will make those Remainers think twice because it is likely the Tories would defeat an unpopular Corbyn if they are (one way or other) not competing for seats with the Brexit Party.
It is also possible Corbyn may not want to fight a general election under circumstances dictated by rebelling Tories. If a vote of no confidence succeeded, that vote would be easy to label as an attempt to prevent British voters from getting what they voted for.
Corbyn would then inherit the label as a usurper for Remain because he would be the immediate beneficiary of an early general election – nevermind Remain’s deeply held suspicions that Corbyn is a closeted Brexiteer who wants freedom from EU spending limits and regulations if Labour wins the next election, but does not want his fingerprints on Brexit.
Corbyn may also reason that it would be better for the opposition to finalize exiting the EU so that he could put his own party’s divisions over Brexit behind him once a general election is called.
If Remain Tories still aren’t swayed by a conditional threat from the Brexit Party not to contest the next election, they will be frightened by Corbyn’s hesitancy to let them write the Labour Party a losing campaign platform.