This sounds like a neat binary: criminal and civil, with significantly different standards of proof. Yet as the historical allegations against Christian Porter earlier this year underscored, the divide blurs when suggestions of potentially criminal conduct arise in civil contexts. The intense public discussion about Porter - and calls for an independent investigation - highlighted the dilemmas raised by this intersection. It also brought unexpected attention to an important employment law principle, the Briginshaw standard, which seeks to square that circle.

While beyond reasonable doubt is commonly understood, Briginshaw - even to lawyers - is complex, contested and confused. But it frequently arises in workplace disputes and particularly APS Code of Conduct investigations involving allegations of serious misconduct or criminal conduct. Understanding the principle's operation is therefore helpful for all public servants involved in managing disciplinary proceedings, and anyone who might find themselves at the centre of such an investigation.

Briginshaw v Briginshaw was a dispute heard by the High Court in 1938. It is somewhat surprising that the case has become such a significant part of Australian law, given it arose in the unusual context of (alleged) adultery and an application for divorce. Victorian couple Clarice Briginshaw and Frederick Joseph Briginshaw had been unhappily married for a number of years when they separated and Clarice moved to Tasmania. After attending a dance in Devonport one evening, Clarice - it was later claimed - had a romantic encounter with a Mr Crawford. Frederick, upon hearing this rumour, filed for divorce on the grounds of adultery ("no fault" divorce was not introduced into Australian law until 1975).

At the time, alleging adultery was a big deal. If proven, the allegation would have a significant impact on Clarice's public reputation. The trial judge applied the criminal standard and ultimately found that Mr Briginshaw had failed to prove Mrs Briginshaw's adultery beyond reasonable doubt.

Mr Briginshaw appealed, on the grounds that the civil rather than criminal standard should have been applied (adultery was not a crime, merely a ground for divorce). Facing the problematic civil/criminal binary, the High Court appeared to create something of a middle-ground: Briginshaw established the principle that in civil matters concerning serious allegations (such as criminal conduct), a decision-maker should not reach an adverse finding without persuasive evidence.

As one High Court judge wrote in Briginshaw, "the satisfaction of a just and prudent mind cannot be produced by slender and exiguous proofs or circumstances pointing with a wavering finger to an affirmative conclusion." Another added: "In such matters 'reasonable satisfaction' should not be produced by inexact proofs, indefinite testimony, or indirect inferences".

In practice, this means that although APS Code of Conduct investigations are determined on a civil, balance of probabilities standard, where the alleged conduct is sufficiently serious to enliven Briginshaw, the decision-making delegate will have to reach a higher state of satisfaction on more persuasive evidence than they would otherwise have to where the allegations were less serious. Accordingly, a public servant cannot be found to have perpetrated criminal conduct via the APS Code of Conduct process without compelling evidence (no "inexact proofs" or "indirect inferences").

Where an APS delegate fails to apply Briginshaw, there may be grounds for judicial review, although there remains some judicial uncertainty as to the intersection between Briginshaw and administrative law. It is not disputed, though, that a failure to apply Briginshaw is centrally relevant in unfair dismissal proceedings. If a delegate decided to dismiss a public servant for committing serious misconduct in circumstances where only a wavering finger pointed towards them having perpetrated the conduct, the dismissal could well be contested in the Fair Work Commission on the ground of lack of 'valid reason'.

By way of example, albeit in the private sector, in the recent case of Bain v CPB Contractors Pty Ltd, a truck driver was dismissed for allegedly driving a vehicle at full speed towards a colleague. The FWC held that the dismissal was unfair due to an absence of sufficiently persuasive evidence. As Senior Deputy President Hamberger observed rather pointedly:

Mr Skinner's allegation against the applicant is very serious. To accept his evidence is to accept that the applicant deliberately drove a very large truck at full speed directly at him and that she only missed hitting him by about 30 centimetres. This implies that the applicant was either trying to murder Mr Skinner, or was driving in such a reckless manner as to place his life in grave danger (perhaps in order to 'intimidate' him, to use Mr Corbett's word). Consistent with the principle in Briginshaw, therefore, one would need very good evidence before accepting that such an allegation is true on the balance of probabilities.

In light of all of this, APS decision-makers overseeing disciplinary processes involving serious allegations (particularly where the conduct could also give rise to criminal liability) would be well-advised to consider the requirements of Briginshaw carefully.

Any public servant who finds themselves as the accused in such an investigation can also take heart from the evidential safeguards imposed by Briginshaw. For that, they can thank rumours of adultery arising from a dance in Devonport in the 1930s, and a very perplexed trial judge in the subsequent divorce application. As the judge conceded: "I have read the evidence several times, and the more I read it the more difficult the case seems ... I do not know what to believe." We will never know whether Ms Briginshaw committed adultery that night, but the legacy of her jilted husband's allegation remains central to our legal system eight decades later.