In a month’s time, lawyers for three former Labour MPs will try to persuade Mr Justice Saunders that he has no jurisdiction to try them on charges of false accounting.

Elliot Morley, David Chaytor and Jim Devine will enter what used to be called a ‘plea in bar’, arguing that they are protected from prosecution on grounds of parliamentary privilege. They and the Conservative peer Lord Hanningfield will not have to tell the court whether they deny fiddling their expenses until the question of jurisdiction has been resolved, certainly by the Court of Appeal and perhaps even by the Supreme Court.

Whatever one may think about whether parliamentary privilege should provide a defence to such charges, there is no doubt that the director of public prosecutions is treating it as a serious issue. Keir Starmer has briefed Lord Pannick QC to argue that the defendants should stand trial in the normal way.

The three former MPs have rightly been granted legal aid and will be separately represented by Edward Fitzgerald QC, Nigel Pleming QC and Gavin Millar QC respectively. Hanningfield did not seek public funding for his defence but has briefed Alan Jones QC.

Morley, Chaytor and Devine base their joint argument on the Bill of Rights 1688 (or 1689 if you reckon that the 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 1688 act is still in force, and there is no doubt that it protects MPs and peers from legal action over what they say in parliament. But what is meant by ‘proceedings’? Does it cover a claim for parliamentary expenses? The defendants say it does.

And who should decide such a question? The former MPs are expected to argue that leaving it to the courts would interfere with separation of the powers, a fundamental constitutional principle under which the judges do not question the way in which parliament conducts its affairs.

But that does not prevent the judges from interpreting legislation once it has been passed. Lady Scotland, the attorney general, told parliament in a memorandum last year that it was for the courts to decide whether the Bill of Rights rendered evidence inadmissible. ‘Article 9 is statute law and its interpretation, as with any other statute, is a matter for the courts,’ she said.

Until now, commentators have assumed that there has been no guidance from the courts on these fascinating questions. They have overlooked a comparable case nearly 20 years ago.Les Huckfield was Labour MP for Nuneaton from 1967 to 1983 and served as an industry minister. From 1984 to 1989, he was a member of the European Parliament. Early in 1991, Huckfield was sent for trial on charges of dishonestly obtaining expenses of more than £2,500 from the European Parliament by deception.

There never was a trial. Mr Justice Morland threw out the indictment, upholding the former MEP’s argument that a prosecution would infringe the sovereignty of the European Parliament. George Carman QC also persuaded the trial judge that a prosecution would also offend the principle of comity, because the parliament had its own procedures for dealing with improper expenses claims. ‘In my judgment,’ said Morland, ‘it would be wholly improper for this court to supplement that procedure by allowing a criminal prosecution.’

The judge added that the money had not benefited Huckfield – who believed that documents supporting the claims were genuine – and had gone instead to a legal defence fund for suspended Labour Party members.

But matters did not end there. Prosecutors attempted to reinstate the trial by seeking judicial review of the judge’s decision.

In response, Huckfield claimed that national courts were bound by EU law to respect decisions of the European Parliament. He also argued that a former MEP had immunity from prosecution in respect of political acts. But these arguments were rejected by the High Court. There was no specific immunity dealing with expenses.

So Morland’s decision was itself quashed. In July 1992, Lord Justice Leggatt ruled that EU states were entitled to prosecute members or former members of the European Parliament accused of obtaining expenses dishonestly. ‘The question whether they were obtained by dishonesty is a question of national law,’ he added. Mr Justice Pill agreed.

Huckfield then appealed to the House of Lords. He and his co-defendants argued that the High Court did not have jurisdiction to review an order of the Crown court. That argument, which had been rejected in the court below, was upheld by the law lords in November 2003. So Morland’s decision on immunity stood, the prosecution was at an end and Huckfield was awarded costs.

As a result, the law lords never considered whether the sovereignty of a parliament would be offended by the prosecution of a former member. The most they said was that the rulings given by Leggatt and Pill would not bind a future trial judge because they had been made without jurisdiction.

Morland’s decision is not binding either, but we can expect the three former MPs to argue that it should be respected. What the judge had wanted to avoid was having to interpret the rules and regulations under which Huckfield had claimed his expenses. ‘In my judgment,’ Morland said, ‘this would involve an infringement by this court of the sovereignty of the European Parliament. For this reason the court declines jurisdiction.’And will we hear those last four words once again? I rather doubt it.