The parts of Allister's speech that the TUV have published in advance include the following:
“But whether it is an Assembly election or the Westminster election, TUV will be there to give voice to the tens of thousands of Unionists across this Province, unrepresented in Stormont, who do not buy into terrorist-inclusive government and who demand devolution compatible with British democratic principles and practices, not the hideous perversion of democracy that is unworkable mandatory coalition.”
That seems to promise that the TUV will stand "across the province" in the Westminster election – including, presumably, in South Belfast and in Fermanagh and South Tyrone.
If the TUV do not stand in these two constituencies then the "tens of thousands of Unionists" there "who do not buy into terrorist-inclusive government" would not be given a voice. The only other unionist parties that they could choose from would be the UUP/UCUNF and the DUP – both of which "buy into terrorist-inclusive government".
If Allister is a man of his word, and if the TUV seriously intends to offer an alternative voice to the unionists that it claims to represent, it must stand in both South Belfast and Fermanagh and South Tyrone. Otherwise it will be allowing parties which "buy into terrorist-inclusive government" to scoop up the votes, and to thereby claim a greater share of the unionist electorate than they deserve – and a mandate for their "terrorist-inclusive government".
But if the TUV stands, then the unionist vote will be split even further, and the two seats may be retained by their nationalist incumbents.
Sometimes 'Experience, Principle, and Integrity' can push you towards having to make very difficult decisions. Will Allister back down (and earn himself a reputation as a paper tiger) or will he stick to his guns and earn himself a reputation as a splitter?
Either choice is bad for the TUV.