An AEC spokesperson said that was because on many forms, a cross represents a check mark, which can indicate yes.

“It therefore leaves it open to interpretation or challenge by a scrutineer,” the spokesperson said.

The AEC said the provision had been in place since 1988, throughout federal elections and referendums, and was the accepted legal advice.

“This is not new,” a spokesperson said.

“The AEC does not have any discretion to simply ignore savings provisions. They are a long-standing legislative requirement.”

The spokesperson said in the 1999 referendum, the rate of informal votes was just 0.86 per cent, and of those, many would not have been related to ticks and crosses.

It expected the “vast, vast majority” of voters would follow the instructions.

All sounds fairly reasonable to me.