Mr Borrows said for Wanganui's two names to become legal, the New Zealand Geographic Board Act must be amended, which will be done through the Statutes Amendment Bill. This is a catch-all bill passed every year by Parliament to tweak existing legislation. Statutes Amendment Bills must be approved by all MPs.
"Last year, the Greens voted against the Bill, but this year they have agreed to vote for it," Mr Borrows said.
"There have been a couple of amendments and hold-ups but I expect the change to be finalised by the end of the year."
Wendy Shaw, the secretary of the Geographic Board, said Wanganui's names cannot be gazetted until the legislation has been changed.
However, Ms Shaw said until the names are gazetted, both can currently be used.
"While the Whanganui/Wanganui alternative naming will not be official until the legislation has passed and the name has been gazetted, as neither name is currently an official name there is no legal reason why either name or both names cannot be used now," she said.