NZ First leader Winston Peters has issued a stern warning to independent MP Brendan Horan to stop using the party's resources.

The political party leader, who was in Tauranga today meeting with Grey Power members before opening the new NZ First office on Cameron Road, remains adamant his expulsion of Brendan late last year was the right thing to do.

NZ First leader Winston Peters at the opening of the new office on Cameron Road tonight.

Speaking to SunLive before the opening, attended by about 60 political supporters, Winston says the opening of the offices is a result of a 'very sad event” from within the party.

Winston expelled Brendan from the NZ First caucus last December, claiming he had lost all confidence in the MP's ability to continue as a member of parliament.

It followed allegations Brendan had misappropriated money from his late mother resulting in an investigation to be brought before the court.

'Brendan Horan shouldn't be in parliament. This is a MMP environment and the public support anti-waka hopping,” says Winston.

'We are down one member from someone who should have resigned from parliament if he had any sense of responsibility.

'He's got our resources and he won't go. He hasn't got a leg to stand on.”

The new offices will house an electoral member 9am-5pm daily with Waikato electoral member Barbara Stewart and Auckland party members making regular visits – along with Winston when parliament is not in session.

Winston says seven weeks out from the political party's 20th anniversary they are stronger than ever, despite the recent setbacks.

The party formed following Winston's resignation from the then-governing National Party. A bi-election on April 17, 1993 was followed by NZ First's formation on July 18.

'This office outlines our commitment to the Western Bay of Plenty.

'We are strong and we have serious prospects for 2014. But this office means the people who want to talk to us and share their concerns we will be open for them.”