Former Labour list MP Louisa Wall could be formally returned to Parliament as early as tomorrow to replace Darren Hughes.

Mr Hughes resigned last month in the middle of a police investigation into a sexual complaint made against him by an 18-year-old university student.

His resignation is effective from midnight tonight.

It will be published in the New Zealand Gazette tomorrow morning, at which point the Governor-General will instruct the Electoral Commission to fill the vacancy.

The Chief Electoral Officer will call the people on Labour's party list to check if they want to become an MP. By law, the officer also checks whether they are still alive and are still party members. The new MP is notified in the Gazette.

Ms Wall will almost certainly replace Mr Hughes because the people ahead of her on the list - Judith Tizard, Mark Burton, Mahara Okeroa, Martin Gallagher and Dave Hereora - are expected to turn down the vacancy.

Labour will today also finalise the roles vacated by Mr Hughes: senior whip and education spokesman. Rick Barker is expected to become the senior whip, though that is a decision for the caucus.

Education will be split between Sue Moroney, who will take the compulsory education role, and David Shearer, who will take the tertiary education role.

The caucus will also formally discuss the Hughes issue for the first time since the resignation. Labour leader Phil Goff says he has no plans to put his leadership to a caucus vote at today's meeting.

He rejected Ms Tizard's comments that he was bringing back the left-right factional split in the party.

Mr Goff said he would not be disappointed if anyone on the list above Ms Wall returned to the caucus, but he had spoken to them and they did not want to go back into Parliament.