The email was alleged to have been sent from prime ministerial adviser Andrew Charlton to Treasury official Godwin Grech, raising the plight of Queensland car dealer John Grant and his possible access to the taxpayer-funded OzCar scheme.

Mr Grant gave Prime Minister Kevin Rudd a free ute.

The AFP statement came following a raid this morning on the home of Mr Grech and Treasury offices.

Mr Grech has been questioned by the federal police about the fake email.

"Preliminary results of those forensic examinations indicate that the e-mail referred to at the centre of this investigation has been created by a person or persons other than the purported author of the e-mail,'' the Australian Federal Police said in a statement.

The interview with Mr Grech was consistent with these findings, police said. The investigation is continuing.

Senior sources believe that Mr Grech's role in the affair is more complicated than previously thought.

The controversy has dominated proceedings in Parliament today.

Opposition Leader Malcolm Turnbull moved to censure Treasurer Wayne Swan over his involvement in the OzCar affair but the motion failed along party lines.

The ABC reported today that the federal police are investigating the posssibility that the email was concocted within the Treasury department.

However, it was reported that police are now investigating a potential link between Paul Lindwall - who left Mr Turnbull's office after the May budget and has worked for Treasury - and Mr Grech.

Mr Grech was kept in a safe house over the weekend by the federal police.

- with Yuko Narushima and AAP