Key Points:

First it was Paintergate. Then Corngate, followed by Speedgate. Now it's Helen Clark and Doodlegate.

A sketch signed by the Prime Minister, who is also Minister of Arts, will go under the hammer at an art auction in Auckland next month.

But the work, an A4-sized ink drawing titled Beehive, Wellington, is not thought to be by her. It is dated August 2001 - two years after Clark first passed off a painting as her own. Originally sold at a charity auction for $1000, that work sparked the Paintergate storm prior to the 2002 election. It was subsequently bought for $5000 by a Labour Party supporter and burned by Clark's electorate secretary.

The Prime Minister was later found by police to have committed a prima facie case of forgery although no charges were laid. She has since confessed to signing at least six other works of art done by others over the past 20 years.

Auctioneer Dunbar Sloane Jnr said Beehive, Wellington, plus a line drawing signed by former MP Matt Robson, were among more than 100 works being sold at a New Zealand "fine art" auction on May 15.

Clark's was almost certainly not genuine, he said, adding it was "somewhat ironic" given it had been Clark, as arts minister, who had recently announced plans to pay artists royalties each time a painting was sold.

"With ink drawings, you get the heavy ink bleeding through the paper. That's happened with the drawing - but not with the signature. That looks like it's been photocopied on."

Approached for comment on the sketch, a spokesman for Clark said the issue had been dealt with comprehensively prior to the 2002 election and there was no further comment to make.

The woman selling the drawings, Margaret Kaa, bought both sketches at a 2001 fundraiser at Ellerslie School, where she is a teacher and Robson was a parent. She was selling them now to "test the waters".

"I've had them for a long time ... I thought I would see if time and events have done anything for their value."

She paid $80 for the 'Clark' and $10 for Robson's drawing of the old Supreme Court.

"The head of the fundraising committee at the time sent some A4 paper to Parliament and just said if anybody would like to draw something, great. Matt did one and got Helen to do one, too.

"At the time we presumed she had done it. I thought it would be neat to have something by New Zealand's first elected woman prime minister, and it was a piece I liked. Now I guess it's a bit of New Zealand history."

She was hanging on to a larger sketch by actor Kevin Smith that she bought for $10 at the same auction. Smith, then also a parent at the school, died after a fall while filming in Beijing in 2002.

Sloane said auction houses occasionally got celebrity artworks through. Sir Edmund Hillary's "quick stick figure type things" were the most sought after. He expected Clark's signature piece to sell for upwards of $2000 and Robson's - "that looks genuine" - for less than $800.