This purely tactical move by ministers may be very significant in how the Fixed-term Parliaments Act is understood and applied. A real constitutional question is whether there is such a thing as a "matter of confidence" any more under the FTPA.
If this vote is announced as matter of confidence and HMG loses, May will have two options. One way of applying the FTPA then would be for the government simply to resign (meaning Jeremy Corbyn would be appointed PM and try to form a government).
A second way would be for May, instead of resigning, to do what she did in 2017 and try in effect to "call" an early election by whipping her MPs to vote for one, under s2(1) and (2) of the FTPA.
If she chose the first option, it'd imply that government had adopted what I've called a "duty to resign" theory of the FTPA. We might see a return to an older type of politics where government changed hands more often without elections.
If she chose the second option, it'd imply the FTPA had changed almost nothing—except to create the slight risk of her trying to "call" an election yet see it rejected by MPs, so leaving her in power after all.
Finally, we must be watchful of politicians' attempts to change the traditional idea of the *government* resigning (or calling an election) after defeat on a matter of confidence into a new concept of *the PM alone* resigning.
It would suit ministers to pretend *the PM alone* resigning is a constitutionally adequate response to defeat on a matter of confidence, and widespread constitutional ignorance might let them get away with it.
But it's not so, and has never been so. If matters of confidence still exist (I think they do) then they are matters of confidence *in the government*. Either the PM resigns in the name of the whole government or there should be an election.
