Craig Thomson.

Vote not wanted ... Craig Thomson. Photo: Andrew Meares

Tony Abbott has been left red-faced after a member of his opposition frontbench sought the ''tainted vote'' of suspended Labor MP Craig Thomson.

Liberal senator Mathias Cormann has admitted he sent a letter to Mr Thomson asking the independent MP to support a Coalition bill to amend government changes to superannuation.

The letter was sent to all crossbenchers and Senator Cormann asked the MPs to ''seriously consider'' the issues raised by the Coalition, saying they were ''worthy of your support''.

Senator Cormann said today it was a clerical mistake that should never have happened.

''It was my mistake,'' Senator Cormann told ABC Radio. ''I should never have written to him.''

Mr Thomson's name would be taken off a database of crossbench MPs used by his office, Senator Cormann said.

The incident is an embarrassing episode for the Coalition, with Mr Abbott determined not to ever accept Mr Thomson's vote.

However, the Opposition Leader's refusal to accept the vote of one scandal-plagued MP will not preclude him from accepting the vote of another, the newly independent MP Peter Slipper.

''I think there's a fundamental different between Peter Slipper and Craig Thomson,'' Mr Abbott said yesterday.

''How [Mr Slipper] votes is up to him, but if he chooses to vote with the Coalition we will be happy to accept that vote.''

Mr Thomson said today he did not believe that six MPs could constitute a ''database''.

''That is not plausible,'' Mr Thomson said.''I've never had a letter from them until October 9 - the day the numbers changed.

''They probably thought they had (Bob) Katter and (former speaker and now crossbencher Peter) Slipper and they needed one more.''

The former Health Services Union official said Mr Abbott was in no position to make statements regarding criminal allegations and a person's suitability to sit in parliament.

''As far as I know, between myself and the Leader of the Opposition he is the only one of the two of us who has faced criminal charges,'' Mr Thomson said.

He was referring to a January 1978 indecent assault charge brought by a female student against Mr Abbott, to which he pleaded not guilty and which a Sydney court dismissed.

''If being charged makes you tainted then he should resign,'' he said.

Prime Minister Julia Gillard said today Mr Abbott was guilt of clear hypocrisy.

''He has his team out there canvassing for Mr Thomson's vote,'' she said. ''It's a clear example of double standards.''

Liberal senator Gary Humphries said it was entirely understandable that a mistake was made.

''Is anyone really seriously suggesting that he [Senator Cormann] was actually going to go out there and solicit the vote of Craig Thomson?'' he told reporters.

''I very much doubt it.''

Opposition Senate leader Eric Abetz said in a choice between a conspiracy and a stuff-up, it was usually the latter.

''Senator Cormann has acknowledged that,'' he said.

''For the journalist who tried to say there was a secret attempt to woo Craig Thomson's vote, I would say 'get a life'.''

It was an accident and something that should not have occurred, Senator Abetz said.

''We all make those sort of mistakes in life.''

Senator Abetz suggested it was Mr Thomson who leaked the letter, showing he was still in cahoots with Labor and seeking to give them every bit of ammunition he possibly could.

''They are saving his political skin so he feels obliged to save their political skin,'' he said.

with AAP

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