Data delays have seen the National Party inquiry into who leaked Simon Bridges' expenses continue for more than a month.

Deputy leader Paula Bennett says investigators PwC only recently received some of what they need from Parliamentary Services.

She says they've been going through MPs' data.

"They had a process to go through as far as getting staff's information, which we're not responsible for as we are not their employers, so they have gone through that process and that is what has taken the time."

Bennett says she's running the investigation from a caucus perspective, but they have not received any reports from the investigators yet.

"We've certainly had no indication from them whatsoever as to who, where, what and what may be happening, as we say they still have a long way to go."

National pushed ahead with its inquiry after the Speaker scrapped a Parliamentary one, due to concerns over the leaker's mental health.