The offices of Winston Peters confidante and trustee of the New Zealand First Foundation Brian Henry were the subject of an early morning raid by the Serious Fraud Office in February, before the Covid-19 lockdown.

Investigators took documents relating to the Foundation, which was said by the Electoral Commission to be in breach of electoral law in that it didn't declare donations that ended up being used for party expenses.

The matter was referred to the police who handed the file over to the SFO for further investigation.

Henry appeared relaxed about the raid, saying he was happy to co-operate with the SFO because the Foundation had nothing to hide. He said all the documents were in a box waiting for them.

Peters has also said in the past the issue had nothing to do with him and the party would be exonerated.

The SFO has, since the lockdown, been conducting the investigation under difficult circumstances but in a statement today said at the outset it planned to have it completed before the September 19 election and that's still its intention.

"However, our actual completion date will be dependent upon our ability to conduct certain interviews as well as other tasks which can only be completed at lower alert levels and the co-operation of those who hold information relevant to our investigation," a spokesman said today.

Peters has always maintained they won't need to interview him because it's got nothing to do with him.

He has said the SFO would not find any evidence of wrongdoing because no such evidence exists – "we have a legal opinion to back up what we have said".

His lawyer Henry is working from his Auckland home and was surprised at being told by Newstalk ZB's Barry Soper of the SFO statement, saying it would seem the media knows more about the investigation than he does.