Has much changed since 1979?
"Such common expressions as
it’s me and was it them? are incorrect, because
the verb
to be cannot take the accusative: the correct expressions are it’s I and
was it they?
But general usage has led to their acceptance, and even to gentle
ridicule of the correct version."
B. A. Phythian,
A Concise Dictionary of Correct English (London: Hodder & Stoughton, 1979).