Strictly speaking, evidence to a select committee covers written evidence produced specifically for the committee, not material which has already been produced for other audiences. It also includes oral evidence heard by the committee, but not remarks made elsewhere.

While committees often do take into account other material already published, they would not normally republish it themselves under the cover of parliamentary privilege. An exception would be when such material is relied on heavily in the committee's report.

A committee would not normally refer to or publish any material relating to a current court case in the UK. This is because the House has a self-denying ordinance not to refer to matters awaiting adjudication in the courts. This sub judice rule is an important way of preventing the legislature and the courts treading on each other's toes during a live case. If the Facebook v Six4Three case was live in the English courts, the DCMS Committee would have been prevented by the sub judice rule from seeking the court papers for the case.

The DCMS Committee's action would only be vulnerable to a legal challenge if a party could argue that the publication was not a proceeding in Parliament - if, for instance, there was no mention in the formal minutes of the Committee that the publication was agreed by the full Committee at a formal meeting. The formal minutes should also record that the documents were reported to the House as evidence for the Committee's inquiry into 'fake news'. The chances are that the DCMS Committee - properly advised by its clerks - will have fulfilled the requirements, and the courts are very reluctant to go into the internal workings of Parliament.

The extent of parliamentary privilege was considered by the courts in R v Chaytor, decided by the Supreme Court in 2010. Three former MPs were unsuccessful in arguing that they should not be prosecuted for fraud in their expense claims on the grounds that their claims were proceedings in Parliament.

The issue of freedom of speech in Parliament - the real basis for maintaining privilege - was also considered by the European Court of Human Rights (ECtHR) in Strasbourg in A v UK in 2002. While the Court upheld the freedom of speech, it issued a mild caution about the adequacy of parliamentary processes for providing a right of reply. That ECtHR jurisdiction will not change on when the UK leaves the EU on 29 March 2019.

It appears that the DCMS Committee followed the standard procedure ('sending for persons, papers and records') in acquiring these documents from Six4Three and Mr Kramer. This involves a series of informal exchanges - when almost all witnesses comply - escalating to formal orders and then a special report to the House notifying it of non-compliance and therefore potential contempt.

However much the prospect of fining and imprisoning recalcitrant witnesses appeals to MPs, the reality is that those powers fell into disuse many years ago - 1666 for a fine, and 1880 for imprisonment.

Under modern human rights principles, such powers could only be revived by legislation and with proper safeguards in the process. Successive Clerks of the House of Commons have long advised Members that this is the case. It is therefore inconceivable that any parliamentary official would have been authorised to threaten Mr Kramer with a fine or imprisonment. Nor would any such official have the power to compel him to come to the House.

The current outstanding case is the refusal of Dominic Cummings, the director of the Vote Leave campaign, to give oral evidence to the DCMS Committee. This awaits an inquiry by the Privileges Committee. It is difficult to see how Mr Cummings could be punished beyond being 'admonished' by the House.

It is unwise to predict how the courts in California would handle these matters. They could not act against a committee of the UK House of Commons for acquiring or publishing the relevant documents. It remains to be seen what view they would take of one party to a current case stating that he was obliged by UK parliamentary powers to hand over the documents to the committee. It may be interesting to observe how a US citizen shows that he was acting under compulsion from the committee. Certainly, before a US Congressional committee, he would have been subject to criminal penalties - as well as entitled to legitimate defences - for refusing to supply evidence.

Recent tests of House of Commons committee powers have involved other US citizens:

• In March 2011, Irene Rosenfeld, Chief Executive Officer of Kraft Foods, based in the USA, refused to appear before the then-Business, Innovation and Skills Committee to explain Kraft's failure to fulfil the undertakings given during its takeover of Cadbury. The assumption is that Ms Rosenfeld avoided visiting the UK. No order to appear before the Committee could have been served on her outside the UK.

• In July 2011, the then-Culture, Media and Sport Committee summoned Rupert Murdoch and others to attend to give oral evidence on News International and phone-hacking, giving rise to widespread media discussion about what would happen if they refused. As the witnesses complied with the summons, the question was not put to the test. The assumption is that Mr Murdoch's business interests in the UK made it worth his while to comply.

At one level, the current DCMS case should be celebrated as an example of the way in which the House of Commons' powers to obtain evidence do work in practice.

At another level, however, there is reason for concern. Controversy has arisen recently over the decision by Lord Hain to name (in the House of Lords) Sir Philip Green as the subject of an interim injunction in live proceedings in the English courts - an apparent breach of the sub judice rule and a questionable use of freedom of speech in Parliament.

For my part, I doubt whether this current DCMS incident will work out badly in the short term. However, I fear that it may weaken the case for Parliament’s necessary powers in the long term. It does not feel like a good precedent.