In some cases evidence may be obtained unlawfully-for example trespassing in the course of entering a site to obtain video or photographic evidence. At common law the courts are not so much concerned by how evidence is obtained but its probative value. Whether such evidence is now admissible will depend on the view taken by the judge or the relevant Acts in your country. In any proceedings the court may refuse to allow the prosecution's evidence to be given if it appears to the court that, with regard to all circumstances , including the circumstances in which the evidence was obtained, the admission of the evidence would have an adverse effect on the fairness of the proceedings that the court ought not to admit it. One must remember that it is usually up to the relevant authorities to initiate proceedings in environmental law.