Three former MPs and a peer will ask the Court of Appeal next week to rule that the Crown court has no jurisdiction to try them on charges of false accounting. Elliott Morley, David Chaytor, Jim Devine and Lord Hanningfield deny supplying false information in support of their expenses claims. In particular, they deny acting dishonestly.

On June 11, Mr Justice Saunders decided that the conduct alleged against the four defendants was not covered by parliamentary privilege and that their trial could go ahead. That ruling was made during the course of a preparatory hearing, held under the Criminal Procedure and Investigations Act 1996. To avoid prejudicing any trial that may follow, only the barest details of such hearings may normally be published.

In this case, however, the judge granted an application by news organisations for permission to report his ruling and comment on it. At the hearing, Andrew Caldecott QC represented every interested journalist in the country – except me. I represented myself and, of course, my readers.

In the event, the judgment did not attract very much press interest. This may be because Saunders was thought by commentators to have come up with the right result. It may be because secret hearings are more interesting to reporters than public judgments.

But the issues raised by the case are fundamental to the rule of law. They are also of great importance to other MPs and peers – not least because Hanningford asserts, as the judge put it, ‘that whatever he has done was wholly consistent with the usages and customs of the House of Lords as can be shown, he says, from the conduct of other peers’.

Saunders began his judgment by explaining a fundamental point: parliamentary privilege is not something that an individual can claim – or waive. It is the privilege of parliament, not of a current or former member. If the defendants had not raised it, the judge would have done so himself.

Even though the privilege belonged to parliament, he continued, it covered the activities of an MP or peer while carrying out parliamentary functions. The best known of these was freedom of speech, enshrined in article 9 of the Bill of Rights 1688. But this was only part of a much broader privilege to be found in common law. That derived from the doctrine of separation of powers and was referred to by the judge as parliament’s ‘exclusive jurisdiction’.

‘How far parliamentary privilege extends to matters ancillary to the main work of parliament is at the centre of [the defendants’] argument,’ Saunders said. If privilege were broadly construed, it might cover the submission of a claim form. But the judge favoured a narrow construction, including only the core activities of parliament.

It had been accepted by the prosecution that the expenses scheme itself was covered by privilege. That meant, for example, that it could not be judicially reviewed by the High Court. Prosecutors also accepted that the administration of the scheme by officials was privileged. But that was as far as they – and the judge – were willing to go.

‘While I accept that the processing of the forms is part of the workings of parliament,’ Saunders said, ‘I see no reason to extend that privilege to cover the submission of the form.’ Claiming allowances was not part of a member’s duty.

But the defendants had a second argument, based on the right to free speech in article 9. ‘The argument is that in order to exercise freedom of speech in parliament, it is necessary to be able to attend; and therefore expenses are ancillary to the exercise of freedom of speech and are included within the definition of proceedings in parliament within article 9.’

There is no doubt that freedom of speech extends beyond the actual words spoken by an MP or peer in the chamber: speaking notes would also be protected. But it seems a bit of a leap to say that, because you need a bus ticket as well as a draft before you can make a speech in parliament, your used bus tickets are as privileged as your old speaking notes.

Ah – said Nigel Pleming QC, defending Chaytor – but what if parliament had required each MP to claim his expenses by making a formal speech, followed by a vote authorising payment? If that mechanism was privileged, Pleming argued, then submitting a claim form would also be covered.

But Saunders wasn’t falling for that old forensic trick: ‘If the system for payment of expenses were the one that Mr Pleming invented, then a claim made in oral submissions to parliament might indeed be covered, but it isn’t the system.’ The judge could see ‘no logical, practical or moral justification for a claim for expenses being covered by privilege’; he could see see no legal justification for it either.

Saunders delivered a pretty robust sort of judgment, avoiding lengthy citations and omitting cases decided any earlier than the 20th century. ‘This judgment is not intended to be a legal dissertation,’ he said modestly. We can expect something rather more sophisticated from the appeal court.

But the real opportunity to recast the common law on parliamentary privilege for the first time in centuries will come when the case reaches the Supreme Court, as I suspect it will. Indeed this is the one case that justifies the creation of that court. If it had come before the House of Lords, we would have seen the limits of parliamentary privilege set by those who were in a position to enjoy them.