The leaders of six opposition parties in the House of Commons are accusing Boris Johnson of “a consistent failure to be honest” – a charge the Prime Minister denies.

Who gets to decide whether someone in power is guilty of lying? And what penalties are in place for those who are found to have deliberately misled parliament or the public?

Code breaking?

In a joint letter to the Speaker of the House of Commons, the leaders of the Greens, SNP, Lib Dems, Plaid Cymru, SDLP and Alliance parties in Westminster refer to two codes of conduct that UK politicians are supposed to follow: the Nolan principles and the Ministerial Code. Both stress the importance of being truthful.

The six leaders wrote: “We believe the Prime Minister consistently fails to meet this standard.  This is not a question of occasional inaccuracies or a misleading use of figures: it is a consistent failure to be honest with the facts, or to correct wrong information at the earliest opportunity when misleading information is given.  This, we believe, amounts to a contempt of the House.”

A Downing Street spokesman responded to the letter by saying: “The Prime Minister follows the ministerial code and Nolan Principles when conducting himself in public life.”

There’s a lot to unpack here: the role of the Speaker, the Ministerial Code, Nolan Principles and contempt of parliament. What do these things mean? And can they be used to hold politicians to account for alleged dishonesty?

The Commons Speaker

People frustrated with debates in the House of Commons often criticise the Speaker for failing to hold politicians to account over allegedly dishonest remarks.

But the MPs who have held this office have been clear over the years that it’s not their job to police the accuracy of debates.

The current speaker, Lindsay Hoyle, issued a strongly worded call last month for MPs to correct the record voluntarily if they make inaccurate statements in the Commons.

But he also stressed that it is not his role to judge whether a statement is true or false, saying: “The Speaker cannot be dragged into arguments about whether a statement is inaccurate or not. This is a matter of political debate.”

Erskine May, the “Bible” of UK parliamentary procedure, states that: “The Speaker’s responsibility for questions is limited to their compliance with the rules of the House. Responsibility in other respects rests with the Member who proposes to ask the question, and responsibility for answers rests with Ministers.”

Ministers regularly do correct the record in parliament, if they have inadvertently said something inaccurate, but it’s not compulsory and the Speaker cannot force them to do it or punish those who refuse.

In fact, the Speaker has much stronger powers to sanction MPs who accuse others of lying in the chamber than those who actually lie: he can order someone guilty of using unparliamentary language to withdraw the remark or leave the chamber.

What about the Ministerial Code?

In his statement, Lindsay Hoyle referred to another piece of official guidance on how Westminster politicians should conduct themselves: the Ministerial Code. Like the rules that govern debate in the Commons, this is also available online.

It states that “holders of public office should be truthful” and that: “It is of paramount importance that ministers give accurate and truthful information to parliament, correcting any inadvertent error at the earliest opportunity. Ministers who knowingly mislead Parliament will be expected to offer their resignation to the Prime Minister.”

But the Ministerial Code is not law, and it is ultimately up to the Prime Minister to decide how to interpret and enforce it.

The convention used to be that ministers offered their resignation if they broke the code. In 2018, Amber Rudd resigned as Home Secretary after “inadvertently” misleading a select committee.

But this convention is not always followed now. In November last year, an inquiry into accusations of bullying against the Home Secretary, Priti Patel, found that she had broken the Ministerial Code.

Ms Patel apologised but did not offer her resignation and Boris Johnson took no further action. As he alone is responsible for enforcing the code, the Home Secretary kept her job.

Only a prime minister can order an investigation into whether the code has been breached in the first place, creating an obvious difficulty if it is the head of the government who is accused of breaking it.

Nolan Principles

The “seven principles of public life” were first set out by Lord Nolan in 1995. The sixth principle is honesty, and the text states that “holders of public office should be truthful”.

Like the Ministerial Code, the Nolan Principles are not law, and no punishment is set out for breaking them.

The principles are taken into account when the authorities are investigating MPs for breaking their code of conduct, but the Parliamentary Commissioner for Standards in the Commons cannot investigate what MPs say when they are in the chamber or probe the actions of ministers.

Contempt of Parliament

The opposition leaders’ letter refers to alleged “contempt of the House” – a phrase which does have some force in law.

You can be found in contempt of parliament if you are caught “deliberately attempting to mislead the House or a committee (by way of statement, evidence, or petition)”.

The law applies to members and non-members – like people giving evidence in front of select committees. But it’s not clear what powers, if any, parliament has to actually punish those who hold it in contempt.

The House of Commons can theoretically fine people for contempt, but no fine has been imposed since 1666.

We have seen in recent years how individuals and even entire governments have been ruled in contempt of parliament but faced no consequences other than public embarrassment.

Despite referring to the law of contempt in their letter, the opposition leaders who accuse Boris Johnson of dishonesty do not appear to intend to pursue a case against him.

After meeting with the Speaker, the leaders said in a joint statement on Tuesday: “A number of possible measures were discussed, including learning from the more transparent and high-profile Scottish model of correcting the record.

“The six leaders will be writing to the Chair of the Procedure Committee to follow up on these discussions.”

The verdict

It’s easier to get thrown out of the House of Commons for calling someone a liar than for lying itself.

Despite often coming under fire from disgruntled viewers, the Speaker of the House does not have any power to police the truthfulness of debates in the chamber.

And other codes of conduct which mention honesty, like the Nolan Principles and the Ministerial Code, are essentially voluntary.

In fact, much of the British political system rests on the assumption that politicians will choose to behave honourably, and there are few sanctions in place for those who defy the conventions.

Dr Alice Lilley from the Institute of Government told us: “Misleading Parliament is a serious matter.

“The convention has always been that ministers who mislead Parliament are expected to resign, and this is set out in the Ministerial Code. But enforcing this convention is more complicated.

“It is ultimately up to the prime minister to decide what happens to ministers judged to have broken the Code.

“And Parliament has very few powers to punish a minister for misleading it. The Commons Speaker might make some pointed remarks that make their irritation clear, but it isn’t their job to determine whether ministers are telling the truth—or the consequences if they aren’t.”