The Director of Public Prosecutions always likes to be as open as possible. This is why Keir Starmer added a cryptic coda to his announcement on 5 February that three Labour MPs and a Tory peer would be tried on charges of false accounting.
"Lawyers representing those who have been charged have raised with us the question of parliamentary privilege," the DPP said. "We have considered that question and concluded that the applicability and extent of any parliamentary privilege claimed should be tested in court."
No doubt Starmer felt he should respond to a well-sourced press report from a month earlier. This said that the three MPs would argue that the House of Commons rulebook on expenses was "privileged" and so could not be subject to scrutiny by the courts.
There was widespread support for the DPP's robust response — which amounted to "See you in court". A fellow Labour MP said on TV that the public would be "aghast if they thought that there was some special little get-out-of-jail card for parliamentarians". Unfortunately, this MP turned out to be the Home Secretary, Alan Johnson. MPs were subsequently warned by the Speaker, John Bercow, that their comments might "risk affecting the fairness of a criminal trial or, furthermore, prevent such a trial taking place". But judges are well used to ignoring Cabinet ministers. If the courts are called upon to decide whether parliamentary privilege provides MPs with a defence, they are not going to be prejudiced by the universal view that it should not.
And does it? Our starting point must be the Bill of Rights 1688 (or 1689 if you reckon that the new year started on January 1). Article 9 says: "That the Freedome of Speech and Debates or Proceedings in Parlyament ought not to be impeached or questioned in any Court or Place out of Parlyament."
The Act is still in force and there is no doubt that it protects members of both Houses from legal action over what they say in Parliament. But what's meant by "proceedings"? Lord Nicholls chaired a joint committee of MPs and peers which recommended in 1999 that the term should be clarified. But Parliament has not done so. The phrase is crucial because, as the committee noted, "article 9 aside, members can be prosecuted for criminal conduct...even when the conduct complained of occurred within the Palace of Westminster."