Prime Minister John Key says reports of Labour MP Rick Barker conducting polling from parliamentary offices using false names was "a serious matter" and needed further investigation.

Mr Key made the comments from Thailand yesterday where he has been attending the East Asia Summit.

But senior Labour whip Darren Hughes said last night that Mr Barker had not misrepresented himself and Mr Key should be careful about what he says.

As with other negative news stories involving Labour, leader Phil Goff has passed responsibility for it on to someone else, this time Mr Hughes.

Mr Hughes said that if the party polled again, it would insist that the volunteers conducting it used their own first names.

Parliament regularly funds party polling on policy issues but they are usually conducted by professional polling companies.

Mr Barker used volunteers for the phone polling, the Herald on Sunday reported yesterday. He confirmed that he had advised volunteers to use different names if it made it easier for them to make calls.

One of the volunteers, a Green Party member, believed it had been unethical of Mr Barker to tell volunteers to use false names and a defunct company, Data Research, which Trevor Mallard and former Labour general secretary Rob Allen set up in the 1990s.

Mr Barker did not return calls last night.

However, Mr Hughes said the woman volunteer who had objected to false names being used had raised the issue and used her own name when she rang people.

The polling had been done over three nights to see what issues were upper-most in voters' minds, issues that could affect party policy and the issues that were raised in Parliament.

Mr Hughes was not sure whether Labour would conduct such polling again using volunteers.

He has said the use of the company name instead of Labour was intended to get a more scientific result, rather than answers that were influenced by the party conducting it.

A spokeswoman for Mr Key said the costs of National's polling were shared between Parliament and the party - policy issue polling was charged to Parliament and party-vote polling was funded by the party.