A judge has paved the way for four parliamentarians to stand trial over expenses fraud allegations. His ruling related to questions about parliamentary privilege.
What is parliamentary privilege?
Parliamentary privilege is one of the oldest rights enshrined in British law and it has a special place in British constitutional history. Privilege developed as a means of stopping a monarch from interfering with the workings of Parliament and it was a key part of the 1689 Bill of Rights.
That Act came within living memory of the English Civil War, which was sparked by a power struggle between King Charles I and Parliament.
The Bill said "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".
What does that mean in practice?
Parliamentarians have the right to say whatever they like in Parliament and they can never be sued for defamation, hauled before the courts or the monarch. Today, it also means that the media can report what is said in Parliament without facing the threat of a libel action.
Erskine May, the official handbook on parliamentary practice, defines privilege as "the sum of peculiar rights… without which [MPs] could not discharge their functions".
So, down the years, privilege has expanded to cover the preparations MPs make for debates, such as their papers, and the questions they table.
What does the Act mean when it refers to protecting "proceedings"?
In 1999, a joint parliamentary committee said that "proceedings in Parliament" needed to be clarified.
That report included a submission from the Crown Prosecution Service which said: "The exact scope of the phrase… is far from clear. Accordingly, it is very difficult to assess the evidential sufficiency of any particular case.
"Clarification of the scope of the phrase would assist by facilitating a more accurate assessment of the evidence available to the Crown in any individual case.
"Naturally, the narrower the scope of the phrase the less parliamentary documentation would be afforded the protection of parliamentary privilege and the easier it would be to prosecute corrupt conduct on the part of members acting in that capacity."
So does it apply to MPs' expenses?
In his June 2010 judgement, Mr Justice Saunders ruled that the three MPs and peer could stand trial because parliamentary privilege did not apply to expenses forms.
The judge said: "I can see no logical, practical or moral justification for a claim for expenses being covered by privilege; and I can see no legal justification for it either."
He said the machinery of Parliament was protected by privilege, but added: "There has to be a line drawn and it has to be drawn somewhere.
"The fact that it is the submission of the claim form that sets the machinery of Parliament in motion does not make it part of that machinery just as putting a coin in a slot machine does not make the coin part of the mechanism of the slot machine just because it initiates the process."
And he added that it was the right of everyone accused of a crime to receive a fair trial before the criminal courts.
"The principle that all men are equal before the law is an important one and should be observed unless there is good reason why it should not apply," he said.
"To do otherwise would risk bringing both the courts and Parliament into disrepute and diminish confidence in the criminal justice system.
"Parliament does not have an effective procedure for investigating and deciding whether a member is guilty or not guilty of criminal charges."
Are there other questions about the workings of privilege?
In November 2008, police raided the parliamentary office of Tory MP Damian Green, now immigration minister, in an investigation into leaks.
A furious row blew up over whether the police had breached parliamentary privilege by entering the Palace of Westminster and seizing protected documents from Mr Green's office.
The police investigation was dropped before there was an opportunity to have an argument in court over what was covered by privilege.
The Green affair led to the Speaker setting out the manner in which detectives can enter Parliament. It also prompted the Commons to set up a committee to examine how and when privilege covers a parliamentarian's correspondence and communications. Its report has not yet been published.
Are British parliamentarians immune from prosecution?
No. There is no law that prevents an MP or peer being prosecuted, unlike in some countries. The most recent case involved Labour's deputy leader, Harriet Harman. She pleaded guilty earlier this year to driving without due care and attention.