Those with a grounding in Latin tend to opt for ‘referenda’ , while those without (who would now appear to be in the majority) opt for ‘referendums’.
Ironically, the latter are correct , and I am reminded of the story told by Angela Rippon, former BBC newsreader, as to how she resolved the matter when Broadcasting House could not.
She deferred to none other than Enoch Powell, classics scholar and sometime Conservative MP.
His advice was that the word ‘referendum’ was not a noun and therefore didn’t adopt the Latin ending, but a gerundive — a verbal phrase meaning ‘that which should be referred’ — which took the familiar English plural ending.
Satisfied, Ms Rippon looked no further.