Not only was she angry at the move to allow GM crops to be grown in WA, she was also denied access to the press conference at which Agriculture and Food Minister Terry Redman announced the decision.

"I can't believe it, I have been denied access to the press function," she said.

"Apparently the conference was a private event open only to those who were invited, who coincidentally were all pro-GM supporters."

Ms Newman was kept in check by a policeman and security officer, who she said told her they had to "protect the dignity of the Premier and Minister".

"The Premier and Minister have been deceptive by claiming segregation of GM canola is possible," she said.

"The trial assessment was done by the Agriculture and Food Department, which has a vested interest in GM crops, as does CBH, which had previously denied any interest in long-term segregation of this product."

Ms Newman was not the only person prevented from attending the conference; so too was GM-Free Consumers Network spokesperson Janet Grogan, who turned up with anti-GM protest signs.

"We are appalled that Mr Redman has ignored the need to introduce more certainty, transparency and public participation into the decison-making process relating to the granting of exemptions to allow the cultivation of GM crops," Ms Grogan said.

"This decision will be detrimental to the state and ignores the wishes of the majority of people and the 24 GM-free shires, five of which are in the minister's electorate, who would like to see WA remain GM-free."