It could be weeks before former Cabinet minister Pansy Wong returns to Parliament to face questions over potential misuse of taxpayer-funded perks as an investigation into the matter has now been extended.

Mrs Wong resigned as a minister after it emerged her husband Sammy worked on business deals while travelling on his wife's taxpayer-funded travel entitlement, breaching the rules of its use.

Mrs Wong took a week's leave from Parliament as Speaker Lockwood Smith instigated an inquiry into the matter, but more than a week later she has yet to return.

Yesterday, Mr Key said he did not know when she would be back but she was unlikely to return before she'd read Parliamentary Service's completed report.

"She'll get a copy in due course that one assumes will put her in a position to answer the questions that you will no doubt pose."

Mr Key did not think it useful for Mrs Wong to return before reading the report as "if she said no comment that would be unacceptable to the media, and as we saw with Phil Heatley, some of the answers he gave initially weren't right because he didn't have all the facts in front of him".

However, the Parliamentary Service, which had said the investigation was likely to take a week or two, said yesterday it was now expected "within the next few weeks", possibly showing it has been widened in scope as Dr Smith said would happen if warranted.

Labour leader Phil Goff said Mr Key should stop making excuses for Mrs Wong and force her to front up.

"She's had more than enough time to think about how much taxpayers' money she's misused to promote her husband's personal business interests."

Meanwhile, Mr Key said even if Mrs Wong was cleared of any serious wrongdoing that prevented her from resuming ministerial duties, there was no way she would be reappointed to Cabinet before a successful outcome for National at next year's election.

While he had expected to decide on her successor this week, demands from the Pike River crisis may postpone that call.