Yes, grammar. From the 19 January edition of Hansard:
Denis MacShane (Rotherham) (Lab): [. . . ] There is no country keener on referendums than Switzerland.The Independent comments:
Michael Fabricant (Lichfield) (Con): Referenda.
Mr MacShane: Referendums. It is a gerund.
Mr Fabricant: It is a gerundive.
Mr MacShane: It is a gerund. Keep your hair on. [. . . ]
Michael Fabricant: [later in the debate, after checking in the dictionary] The right hon. Member for Rotherham (Mr.MacShane) may have inadvertently misled the House earlier, and I am sure that he would wish to retract that. As the word “referendum” means “things to be referred”, according to the “Oxford English Dictionary”, it is indeed a gerundive and therefore the plural should be “referenda”. “Referendums” is acceptable in modern usage, though wrong.
Hon. Members: Withdraw!
The “keep your hair on” bit was a little cruel, because Mr Fabricant is famous for having a topping of blond hair which a lot of people think is not real. [. . .]Well, doh.
But, should you need to ask, [. . . ] a gerund has no plural form in Latin, therefore if “referendum” were a gerund, you could not say “referenda”, but since it is in fact a gerundive, “referenda” is correct. Correct, if a little pretentious. But I expect you already knew that.