In Ireland, until 1737, indictments were presented to the accused in latin. The repealing act was 11 Geo. II, c.6.
Currently the principal Act governing the framing of Irish indictments is the Criminal Justice (Administration) Act 1924, which contains in a Schedule and an Appendix, the general rules for framing indictments.
The concept lying behind the modern approach is the principle of legality. This means that a person aught not to be charged with an offence unless the charged offence springs from a pre-existing rule of law where the behaviour has been clearly and precisely prohibited.
The history of this idea probably starts with Beccaria and is found expressed in Article 15.5 of the Irish Constitution and Article 7 (1) of the European Convention on Human Rights and Fundamental Freedoms.
Given the length of time this issue has been to the forefront of judicial matters it would be a surprise to find a charge that does not conform to these principles.
Or perhaps not; see King v Attorney General  IR 223, where the only section of the Vagrancy Act 1824 still extant was declared unconstitutional, There, Judge Kenny said â
t is a fundamental feature of our system of government by law (and not by decree or diktat) that citizens may be convicted only of offences which have been specified with precision by the judges who made the common law, or of offences which, created by statute, are expressed without ambiguityâ¦ In my opinion, both governing phrases (in s. 4 of the Vagrancy Act 1824) âsuspected personâ? and âreputed thiefâ? are so uncertain that they cannot form the foundation for a criminal offence.
For years prior to 1981 [the date of the judgment] young barristers were enjoined by their seniors to attack the use of Section 4. In short, the ground was laid and perceptions clarified long before the Section fell.
Which brings me to the question; when is a police officer acting in the due course of his/her duty?
Not everything s/he does is in the course of duty (not to speak of the due course of duty).
Therefore a charge adopting the wording of Section 19 (3) of the Criminal Justice (Public Order) Act 1994:
(3) Any person who resists or wilfully obstructs a peace officer acting in the execution of his duty or a person assisting a peace officer in the execution of his duty, knowing that he is or being reckless as to whether he is, a peace officer acting in the execution of his duty, shall be guilty of an offence.
-without specifying what was the alleged duty being obstructed or resisted is surely vague and uncertain and bad.