The third edition of Fowler (1988) has
In BrE the subjunctive
mood is most likely to be found in
formal writing or speech [apart from
some formulaic uses], and particularly (the so-called
mandative subjunctive) after verbs such as
demand, insist, pray, recommend, suggest,
and wish; nouns and adjectives such as
demand, essential, important, insistence, proposal,
suggestion, vital, and wish; and a
number of conjunctions, such as
although, as if, as though, if, unless, etc. But
it is seldom obligatory, and indeed is
commonly (?usually) invisible because
the notionally subjunctive and the indicative
forms are identical.
It's not obligatory apart from some formulaic uses, which Fowler lists as including
be that as it may; so be it; bless my
soul; come what may; far be it from me to;
God forbid (that); God bless you; God save
the Queen, etc.; heaven forbid/forfend (that);
heaven help us; So help me (God); Thy Kingdom
come; long live the Queen, etc.; perish
the thought; the powers that be; serve you
right; suffice it to say that; woe betide;
the fixed phrase as it were, in the
sense 'in a way, to a certain extent' [when] the
phrase is invariable.
The subjunctive mood* is available, and maybe even desirable in formal writing; but it's not incorrect if it's not used.
*Fowler defines the subjunctive mood as "a verbal
form or mood expressing hypothesis,
usually denoting what is imagined,
wished, demanded, proposed, exhorted,
etc. Its main contrast is with the indicative
mood." Fowler also notes "The subjunctive
mood is one of the great shifting sands
of English grammar. Its complexity over
the centuries is such that the standard
reference work on historical English syntax
by F. Th. Visser (4 vols., 1963–73)
devoted 156 pages to the subject (Visser
called it the 'modally marked form') and
listed more than 300 items in its bibliography."
There do exist, even in these hallowed halls of ELU.SE, those who eschew the term.