The Big Question: What is parliamentary privilege, and is it being abused?

Why are we asking this now?

Three Labour MPs, Elliot Morley, David Chaytor, Jim Devine and a Tory peer, Lord Hanningfield, have been charged with false accounting over their expenses claims. They deny the offences and are trying to avoid a criminal trial by invoking the 1689 Bill of Rights which gives force to parliamentary privilege. This is the privilege which stops MPs and peers from being sued for defamation.

What's that got to do with criminal prosecutions under the Theft Act?

The modern understanding of parliamentary privilege relates to immunity from litigation for words spoken in the House of Commons. But it also has a broader historical meaning, grounded in the evolution of our constitution which can be open to legal interpretation. It is that interpretation which the MPs' lawyers will be hoping to use to their clients advantage.

What are the origins of parliamentary privilege?

They date back to the English Civil War when Parliament was fighting for the right to self-governance and independence from the monarchy.

But it wasn't until 1689 when the Bill of Rights established the rights of parliament after the so-called Glorious Revolution that it became enshrined in law. Article 9 of the Bill of Rights states that "the freedom of speech and debates or proceedings in parliament ought not to be impeached or questioned in any court or place out of Parliament". In those days the law was subject to the will of the King. And it was interference from the sovereign that Parliament sought to rid itself. Parliament held MPs to account by its own strict laws which ran in tandem with the criminal and civil courts. The rule of parliament was absolute.

How have the rules of privilege changed?

The decline of the monarchy has enabled Parliament to surrender some of its jurisdiction to the courts. MPs accused of criminal offences are no longer dealt with by the authorities of the House of Commons and instead face the full force of the law. Since 1979 at least 10 MPs have been sent to prison, usually for not paying fines incurred when they were conducting political protests in Northern Ireland. Nevertheless privilege still grants MPs immunity from arrested on civil matters within the grounds of the Palace of Westminster. Other historical privileges include an MP's right not to be impeded when entering the Commons.

When was the last time parliamentary privilege was invoked?

It was the Damian Green MP affair which last brought Parliament into conflict with the law. Mr Green was arrested by the Metropolitan Police at his constituency home on 27 November 2008 on suspicion of "aiding and abetting misconduct in public office" and "conspiring to commit misconduct in a public office".

In a statement to Parliament in December 2008, Speaker Michael Martin, responsible for the security of the Palace of Westminster, stated that, although the Police undertaking the search had neither presented a search warrant nor given (what Mr Speaker Martin said was) the requisite advice that such a warrant was necessary, the search of the Parliamentary office had been undertaken with express written consent from the Serjeant at Arms, who had signed a consent form without consulting the Clerk of the House. The arrest of a senior opposition politician (and former journalist) on matters connected with access to confidential information for release to journalists raised concerns about the protection of MPs under the law.

How did the case help clarify parliamentary privilege?

After the arrest in December 2008 the Speaker explained his actions to the Commons, telling MPs that parliamentary privilege has never prevented the operation of the criminal law. He referred to the Joint Committee on Parliamentary Privilege which in its report in 1999 said that the precincts of the House are not and should not be "a haven from the law". The committee went on to say that in order to carry out public duties without fear or favour, Parliament and its members and officers need certain rights. Parliament needs the right to regulate its own affairs, free from intervention by the government. "Members need to be able to speak freely, uninhibited by possible defamation claims. These rights and immunities, rooted in this country's constitutional history, are known as parliamentary privilege," said the committee.

What sort of defence will the four politicians run?

We won't know that until the start of the trial. All that has been said by the Crown Prosecution Service is that they are anticipating lawyers claiming breach of privilege. Keir Starmer QC, the director of public prosecutions, said last week: "Lawyers representing those who have been charged have raised with us the question of parliamentary privilege. We have considered that question and concluded that the applicability and extent of any parliamentary privilege claimed should be tested in court."

This issue will be determined as a preliminary legal point before the start of the trial. The MPs' argument may be that the rules governing parliamentary expenses are the sole responsibility of Parliament and are therefore outside the jurisdiction of the courts. To support this contention their lawyers will point to the established Parliamentary rules and committees which have overseen the expenses claiming process for hundreds of years.

What do legal experts think of this defence?

Most lawyers regard it as a novel point in law without precedent which raises important questions about the inherent right of parliament to govern its own affairs. Michael Smyth, head of public policy at international law firm Clifford Chance, says that because parliamentary privilege has its origins in the "complicated constitutional settlement" between Parliament and Sovereign it may not afford the same meaning as it did some 400 years ago.

"In the modern era the term has tended to be confined to a literal parliamentary privilege to speak frankly of opinions which will not be subject to the civil courts. This is the same as a witness in a court." But he adds that this may be the first time that defence of privilege had ever been advanced as a defence to an allegation of over-claiming on expenses. "If they win on this point then it is a strike out argument and the whole prosecution falls."

How have the leaders of the two main parties reacted to the use of privilege?

The government says that MPs are not exempt from criminal law and that it does not think a new law is necessary. But it says it would, "if necessary", legislate to remove any ambiguity. David Cameron says he would pass a Parliamentary Privilege Act to clarify the law. The joint committee on parliamentary privilege proposed legislation on this in 1999, but the government has not implemented its recommendations.

Should the accused be allowed to use a defence of parliamentary privilege?

Yes...

*Parliamentary matters are for parliament to deal with

*Questions about the limits of parliamentary privilege should be heard in public

*A defendant who is unable to fully argue his defence is denied a fair trial. It is up to the court to rule on the admissibility of a possible defence

No...

*It is a long established principle that no one is above the law – including MPs

*By hiding behind parliamentary privilege the parliamentarians are bringing their office into disrepute

*Parliamentary privilege was never intended to help politicians escape the criminal law