Mr Thomson was referred to the committee by the Coalition in May for failing to declare that Labor had paid his legal bills incurred during a defamation case with Fairfax (owner of this website) and a drawn-out investigation by Fair Work Australia.

The Coalition had also referred Mr Thomson for allegedly misleading Parliament during his response to FWA findings that he had misused union funds for escort services, lavish meals and shopping sprees.

In a tit-for-tat move, Liberal backbencher Craig Kelly, who holds the south-western Sydney seat of Hughes, was referred by the manager of government business, Anthony Albanese, over a range of allegations, including his failure to declare on his register of interests his directorship of several companies.

In a statement to the House of Representatives after question time today, committee chairwoman Yvette D'Ath said the committee — which holds unrivalled powers to discipline MPs for breaches of parliamentary rules — had deemed there ''were no grounds for further investigation'' into Mr Thomson and Mr Kelly over the alleged failure of declarations.

Ms D'Ath also informed Parliament the committee were unable to find the source of a leak to The Age's political editor Michelle Grattan who reported in May details of a meeting in which the committee resolved to write to manager of opposition business Christopher Pyne, who raised the privileges matter, and ask him to specify where he thought Mr Thomson had deliberately misled the house.

Grattan also revealed Labor members of the committee would not agree to a Coalition push for the committee to advertise immediately for witnesses and submissions.

Only four Liberal members sit on the House privileges committee, with six Labor MPs (including the chair) and independent Tony Windsor rounding out the numbers.

Members do not traditionally rule along party lines.

Follow the National Times on Twitter