Immunities and powers part of ordinary law
In Australia parliamentary immunities and powers are part of the ordinary law by virtue of section 49 of the Constitution. The only way in which the Houses can definitely alter their immunities or powers is by passing legislation, as authorised by that section. The courts uphold parliamentary immunities by preventing any violation of those immunities in the course of proceedings before the courts, and they uphold parliamentary powers, especially the power to punish contempts, in any test of the legality of the exercise of those powers.
This reflects the evolution of the law in the United Kingdom. The law in respect of the immunities and powers of the Houses of the British Parliament was originally formulated by the two Houses. They also claimed to be the only courts which could interpret and apply that law. The ordinary courts rejected this claim, and maintained that the law of parliamentary immunities and powers was part of the ordinary law and could be interpreted and applied by the courts.
There were some famous clashes between the Houses and the courts resulting from this difference of view. After the middle of the 19th century, however, the Houses tacitly abandoned their claim and acquiesced in the view of the courts that the law is indivisible. For their part, the courts accepted and adopted the law as it had been expounded by the Houses. It is now regarded as firmly established in Britain that parliamentary immunities and powers are part of the ordinary law and are interpreted and upheld by the courts. This means that many of the resolutions and other precedents belonging to that earlier period are now irrelevant. For example, the declaration by the British Houses in 1704 that they could create no new privileges is sometimes given great importance in discussions in Australia. That resolution, however, belongs to the period when the Houses regarded themselves as courts formulating their own law, and it is now of no significance, because only the courts can say what powers and immunities exist and what is their extent.
In a few rare cases in recent times the British House of Commons has determined the extent of parliamentary immunities. One instance was the Strauss case in 1957, in which the House decided, contrary to the finding of its Committee of Privileges, that the writing of a letter to a minister was not included in proceedings in Parliament. Had the question been determined in court, the court might have taken a different view; if a court had made the decision, it would have been binding as a matter of law, unless overturned by a higher court.
The law of parliamentary immunities and powers is therefore not different from other branches of the law. Law and parliamentary practice, however, are distinct. The Senate's Privilege Resolutions, for example, which regulate the practices of the Senate in relation to privilege matters, are not part of the law and are not subject to interpretation or application by the courts.