The Federal Opposition says an Australian Federal Police (AFP) investigation shows a leak that revealed a hole in the Coalition's election costings must have come from Treasurer Wayne Swan's office.

During the election campaign a Treasury analysis about the cost of the Government's National Broadband Network was leaked to a newspaper.

The leak showed an $800 million hole in the Coalition's election costings and prompted the Opposition to refuse to submit its policies to Treasury for costing.

The AFP was asked to investigate, but today issued a statement saying it would not be taking any further action because there was no evidence a Commonwealth offence had been committed.

A spokesman for Mr Swan says the police investigation has revealed the Opposition's claim for what it was - a political stunt by the Liberal Party to hide its incompetence.

Opposition finance spokesman Andrew Robb says the reason the AFP did not identify any Commonwealth offences is because whoever leaked the document was authorised to distribute the material.

He says the only people authorised to do so would be the Treasurer or one of his senior staff.

"It is clear from the police investigation that Wayne Swan and his office were up to their necks in the leaking of this confidential Treasury document," he said.

"They have deceived the Australian people and they have allowed the reputation of Treasury to be seriously brought into question now for several weeks for no good reason."

Mr Robb says the costings leak has left a cloud over both the Treasury and the Coalition.

"There is no doubt that public opinion of our costings process was materially influenced by this piece of deception and dishonesty by the Treasurer," he said.

"Our actions have been totally vindicated now by this action which is unbefitting of the office of the Deputy Prime Minister."