Parliamentary privilege is a legal immunity enjoyed by members of certain legislatures, in which legislators are granted protection against civil or criminal liability for actions done or statements made in the course of their legislative duties. It is common in countries whose constitutions are based on the Westminster system.
In the United Kingdom, it allows members of the House of Lords and House of Commons to speak freely during ordinary parliamentary proceedings without fear of legal action on the grounds of slander, contempt of court or breaching the Official Secrets Act. It also means that members of Parliament cannot be arrested on civil matters for statements made or acts undertaken as an MP within the grounds of the Palace of Westminster, on the condition that such statements or acts occur as part of a proceeding in Parliament—for example, as a question to the Prime Minister in the House of Commons. This allows Members to raise questions or debate issues which could slander an individual, interfere with an ongoing court case or threaten to reveal state secrets, such as in the Zircon affair or several cases mentioned by the Labour MP Tam Dalyell.
There is no immunity from arrest on criminal grounds, nor does the civil privilege entirely extend to the devolved administrations in Scotland or Wales. A consequence of the privilege of free speech is that legislators in Westminster systems are forbidden by conventions of their House from uttering certain words, or implying that another member is lying. (See unparliamentary language.)
The rights and privileges of members are overseen by the powerful Committee on Standards and Privileges. If a member of the House is in breach of the rules then he/she can be suspended or even expelled from the House. Such past breaches have included giving false evidence before a committee of the House and the taking of bribes by members.
Similar rights apply in other Westminster system countries such as Canada and Australia. In the United States, the Speech or Debate Clause in Article One of the United States Constitution provides for a similar privilege, and many state constitutions provide similar clauses for their state legislatures.
Parliamentary privilege is controversial because of its potential for abuse; a member can use privilege to make damaging allegations that would ordinarily be discouraged by defamation laws, whether or not those allegations have a strong foundation. A member could, even more seriously, undermine national security and/or the safety of an ongoing military or covert operation or undermine relations with a foreign state by releasing sensitive military or diplomatic information.
The ancient and undoubted rights and privileges of the Commons are claimed by the Speaker at the beginning of each new Parliament. The privileges are only codified in Erskine May: Parliamentary Practice and the House itself is the only judge of its own privileges. Most of those specifically claimed are practically obsolete, but others remain very real:
There is an absolute common law privilege for papers circulated among MPs by order of the House (Lake v. King (1667) 1 Saunders 131). This is extended to all papers published under the House's authority, and to correct copies by the Parliamentary Papers Act 1840. The Act also extends qualified privilege to extracts.
In addition to applying to members' speech within the chamber, parliamentary privilege also applies to select committees. Written and oral evidence given to, and published by these committees is also subject to the same absolute privilege as parliamentary papers. This means that any evidence given by a witness to a select committee may not be used against them or any other person in a court of law, whether for civil or criminal proceedings. This privilege only applies, however, if the committee has formally accepted it as evidence and does not apply to materials published before they were given to the committee.
In Canada, the Senate and House of Commons and provincial legislative assemblies follow the definition of parliamentary privilege offered by the British parliamentary authority, , which defines parliamentary privilege as "the sum of the peculiar rights enjoyed by each House collectively as a constituent part of the High Court of Parliament, and by Members of each house individually, without which they could not discharge their function... the privileges of Parliament are rights which are absolutely necessary for the due execution of its powers. They are enjoyed by individual Members, because the House cannot perform its functions without unimpeded use of the service of its Members, and by each House for the protection of its members and the vindication of its own authority and dignity." Parliamentary privilege can therefore be claimed by Members individually or by the House collectively.Erskine May's Treatise on The Law, Privileges, Proceedings and Usage of Parliament
The rule for when parliamentary privilege applies is that it cannot exceed the powers, privileges and immunities of the imperial parliament as it stood in 1867, when the first constitution was written.
The Supreme Court of Canada has previously dealt with the question of parliamentary privilege in . In that case, the Court made these observations about parliamentary privilege:
"Privilege" in this context denotes the legal exemption from some duty, burden, attendance or liability to which others are subject. It has long been accepted that in order to perform their functions, legislative bodies require certain privileges relating to the conduct of their business. It has also long been accepted that these privileges must be held absolutely and constitutionally if they are to be effective; the legislative branch of our government must enjoy a certain autonomy which even the Crown and the courts cannot touch. The privileges attaching to colonial legislatures arose from common law. Modelled on the British Parliament, they were deemed to possess such powers and authority as are necessarily incidental to their proper functioning. These privileges were governed by the principle of necessity rather than by historical incident, and thus may not exactly replicate the powers and privileges found in the United Kingdom.
Recent cases of parliamentary privilege in Canada adjudicated by the courts include:
In 1904, the Parliament of Western Australia imprisoned John Drayton for three weeks for a breach of parliamentary privilege.
In 1955, a newspaper proprietor Raymond Fitzpatrick and his editor Frank Browne were jailed by the Australian House of Representatives for three months for what the House considered a gross breach of parliamentary privilege. The public and most commentators, then and since, felt the punishment far outweighed the crime.
This privilege was considered in the South Australian Employment Court in the case of Kosmas v Legislative Council (SA) and Others  SAIRC 86. The Court found that employment statutes apply to the Parliament and therefore employees can seek judicial relief for matters such as unfair dismissal or workers compensation.
The New Zealand Parliament accords its members parliamentary privilege like its British counterpart, preventing members for being sued or prosecuted for anything that was said on the floor while in session.
Helen Suzman used parliamentary privilege in her anti-apartheid campaigning. Helen Suzman reported during a 1994 interview that she was able to get around state of emergency rules applied against press reporting of violence in the country by asking questions in parliament about the subjects that the press were forbidden from talking about. South African legislation allowed anything said in parliament to be published in spite of emergency legislation. She commented on the hypocrisy of anti-apartheid campaigners criticising her for fighting apartheid from the inside in this way, yet publishing information revealed by her by means of parliamentary privilege.
The Parliament of Singapore accords parliamentary privilege to it members, preventing them from being sued or prosecuted for anything said on the floor while parliament is in session, or during any parliamentary committee meetings.