Labour has pledged to seek to have ministers held in contempt of parliament if they fail to publish the full legal advice on Brexit, as demanded in a motion passed in the Commons last month. What does this mean and how would it work?

What is contempt of parliament?

In simple terms, it is an action taken by an MP or someone else to hinder or obstruct the work of parliament, for example giving false evidence to a parliamentary committee or failing to provide information or testimony as requested by the chamber.

What are the potential punishments?

For MPs it is suspension or even, in the most serious cases, expulsion. The powers are more hazy when it comes to non-members, as shown with recent cases such as attempts by the culture, media and sport committee to force the former Vote Leave chief Dominic Cummings to appear before it.

The serjeant at arms, the official responsible for order in the Commons, can be sent to serve a warrant, as used last month to seize Facebook documents. But if a witness refuses to appear, as with Cummings, there are few realistic options. The last time a non-MP was detained by the Commons was in 1880.

Are MPs ever punished for contempt?

It does happen, but rarely. The great majority of suspensions in the Commons since the war have been for disorderly conduct. In 1947 a Labour MP, Garry Allighan, was expelled for contempt after writing an article that wrongly claimed other MPs took bribes in exchange for information.

In 2002, Labour’s Keith Vaz was suspended from the Commons for a month for contempt after it was found he made false allegations to police about a woman who had lodged a complaint about him.

The most recent contempt suspension was that of the Tory MP Justin Tomlinson, for two sitting days in 2016, for leaking a draft committee report.

Last year David Davis, the then Brexit secretary, was spared a contempt case in a row about the delayed release of Brexit impact assessments after the Commons Speaker, John Bercow, decided to not refer him for investigation.

How does the process work?

If Labour believes the government has been in contempt over the legal advice it must make a formal complaint about the minister or ministers deemed responsible, which would then be considered by Bercow.

If Bercow then said there was a case to answer, he could permit a motion from the complainant to have the case referred to the Commons committee of privileges, a cross-party group of MPs. It would be up to the committee to formally investigate any alleged contempt, and to produce a report containing a conclusion and, if needed, a recommended punishment, which would have to be approved by the Commons.