The law of evidence generally concerned with pre trial and trial stages.
In pre trial stage, the law of evidence is focused on the collection of evidence.
In trial stage, the law of evidence is directed on the presentation and used of the evidence.
For instance, the Police and Criminal Evidence Act ( PACE) 1984 and its Codes of Practice are concerned with the set of rules of the police's conduct in obtaining evidence related to the commission of an offence.
Any issue of non compliacne with the PACE Act (1984) and its Code of Practice will affect the reception of evidence during trial.