WA Premier Colin Barnett has dismissed Labor's call for an immediate internal investigation into whether the name of the bidder for a major rail project was leaked from within Transport Minister Dean Nalder's office.

Key points: Dean Nalder's office has given ASIC documents relating to a possible information leak

Dean Nalder's office has given ASIC documents relating to a possible information leak "Leak" relates to suspicious share trading in NRW Holdings

"Leak" relates to suspicious share trading in NRW Holdings NRW Holdings is preferred tenderer to build Forrestfield Airport Rail Link

NRW Holdings is preferred tenderer to build Forrestfield Airport Rail Link Government rejects calls for immediate internal inquiry

The Australian Securities and Investment Commission is investigating a 30 per cent jump in the share price of NRW holdings three days before it was named as the preferred bidder for the $2 billion Forrestfield-Airport Link.

The Government and Opposition today traded blows in Parliament over the issue with Labor accusing Mr Nalder of not taking the issue seriously, and demanding answers over who knew about the bidder before the official announcement was made.

Shadow treasurer Ben Wyatt wanted the Government to launch an immediate investigation.

"ASIC are clearly concerned that ... the movement of information from your evaluation committee, to the steering committee, through the Department of Premier and Cabinet, the Department of Treasury, and the Transport Department has been compromised," Mr Wyatt told Parliament.

Labor accused of 'gutter innuendo'

Premier Colin Barnett dismissed the push for a separate internal investigation and said it was not even clear, at this stage, if insider trading based on leaked information had driven the share spike.

"Was there insider trading? I don't know. The Minister doesn't know. Let's let ASX and ASIC determine if there was insider trading and if there was information leaked and in obtained in some way and from whom," Mr Barnett said.

Mr Barnett said the Opposition's attempts to pursue the Government could compromise existing investigations

He said his office, Mr Nalder's office, and other Government agencies were cooperating fully with the investigation, and challenged the Opposition to produce any evidence it had.

"If you have any information, which you do not — all you can do is the scummy, in the gutter, innuendo," Mr Barnett said.

Spike may be pure market speculation: Nalder

Mr Nalder said it still was not clear what had triggered the spike.

"It's not just necessarily to do with the department — it could be anybody for any reason. It could be purely speculation in the marketplace," he said.

"To actually suggest that there are allegations of inappropriate behaviour at this point is premature."

Mr Nalder maintained he received the information about the preferred tenderer after the price jump.

"I can assure you categorically that we received that information well and truly after that share price hike," he said.

"There can be no assertion that anybody in my ministerial office had anything to do with that.

"We are not under investigation. We are assisting ASIC in the investigation."

Nalder staffer sat on tender committee

Mr Nalder confirmed a member of his office employed by the Public Transport Authority sat on a committee assessing the tenderers.

"He was specifically removed from the committee when the final proponent was discussed to work our the final tenderer," he said.

He challenged the Opposition to produce evidence pointing to a leak or any misconduct by Government departments or staff.

"There are accusations of improper behaviour by me, my staff, and my department, and I haven't seen anything, one shred of evidence, that anything has been done wrong," he said.

"At this point in time, there has been nothing from ASIC that would suggest concern for the State Government.

"There has been nothing provided by ASIC that there should be concern about any individual that is employed by the State Government."