Public anger from the 9-month-old MPs’ expenses scandal is still very real. From the revelations in the Telegraph last year right through to this week’s publication of the Legg report, the issue of MPs’ expenses has never really been that far from the minds of the electorate, and it is certain to be an issue in the next General Election, which is only a couple of months away.

After lengthy and detailed police investigations, we now have the prospect of at least three MPs and a Peer of the Realm appearing in court to answer specific charges under the Theft Act 1968. I’m not going to comment on the individual cases or the circumstances surrounding the charges. That’s for the courts to now adjudicate upon, but there is an issue I do want to explore, and that is the notion of Parliamentary privilege.

My own basic (and I have to admit, limited) understanding of Parliamentary privilege is that it is in place to ensure that MPs’ may speak freely in the chamber of the House of Commons without the fear of legal action. Things that I could be sued for saying outside parliament, I am able to talk about freely in the House. This is a precious facility that shouldn’t be abused or misused by parliamentarians.

The history of Parliamentary privilege goes back to the period immediately before the English Civil War when King Charles I ordered the arrest of five ‘troublesome’ Members of Parliament. The MPs escaped arrest and the event became a defining moment in the protection of Members from the other branches of government.

The concept of Parliamentary privilege, certainly as we understand it today, was further codified in the 1689 Bill of Rights which gives protection to MPs “for words spoken or things done in the course of, or for the purposes of or incidental to, any proceedings in parliament”.

If the newspaper reports are correct, it is under this provision in the Bill of Rights that the Members in question are seeking protection. The Director of Public Prosecutions yesterday conceded that the reach of Parliamentary privilege is unclear in this respect.

Quite frankly it is an abuse of this historic freedom to argue that because the expenses regime was a Parliamentary function (of course now it is a function of the Independent Parliamentary Standards Authority) it is therefore covered by privilege.

The forthcoming court hearings may be of real constitutional significance – redefining the whole notion of Parliamentary privilege for the modern age.