Relevancy is a concept which runs through the Evidence Act. In fact, the major parts of the Act deal with the relevancy. According to section 5 of the Act, it provides:
Evidence may be given in any suit or proceeding of the existence or non- existence of every fact in issue and of such other facts as are hereinafter declared to be relevant and no others.
This section laid down the principle that the evidence may be given only of facts in issue and other facts declared by this Act to be relevant and of no others. And the facts declared to be relevant by this Act are contained in section 6 until 55 of the Act. This section must be read with section 136(1) of the Act. But, there are certain matters that do not require to be proved by evidence. It is based on the case of
Pembangunan Maha Murni Sdn Bhd v Jururus Ladang Sdn Bhd  2 MLJ 30, 31(SC):
Now the general rule is that all the facts in issue and relevant facts must be proved by evidence. But, there are two classes of facts which need not be proved, viz. a) facts judicially notice and (b) fact admitted. The exceptions are dealt with by sections 56,57and 58 of the Evidence Act 1950 under the title ‘facts which need not be proved’.
The general rule is all the relevant evidence is prima facie admissible. However there are exceptions to this rule. In R v Turner  1 ALL ER 70, 74 (CA):
“Relevancy however does not result in evidence being admissible: it is a condition precedent to admissibility. Our law excludes evidence of many matters which in life outsides the courts sensible people take into consideration when making decisions. Two broad heads of exclusion are hearsay and opinion”.
Meanwhile, according to Lord Simon of Glaisdale in R v Kilbourne  AC 729,757) HL):
“Not all admissible evidence is universally relevant. Admissible evidence may be relevant to one count of an indictment and not to another. It may be admissible to rebut a defenses but inadmissible to reinforce the case for the prosecution”.
In order to admit any fact as evidence it must be receivable under this Act or by virtue of a specific provision in any other Act. According to Lord Atkin in Sris Chandra Nadra v Rakhalananda AIR 1941 PC 16, 20 (PC):
“What matters should be given in evidence as essential for the ascertainment of truth it is the purpose of the law of evidence whether at common law or by statute to define. Once a statute is passed which purports to contain the whole law it is imperative. It is not open to any judge to exercise a dispensing power, and admit evidence no admissible by the statute because to him it appears that the irregular evidence would throw light upon the issue. The rules of evidence whether contained in a statute or not are the result of long experience choosing no doubt to confine evidence to particular forms and therefore eliminating others which it is conceivable might assist in arriving at truth.”
ILLEGALITY IN OBTAINING AN EVIDENCE
As general, the court is not concerned with how the evidence was obtained. Even if the evidence was illegally obtained it is admissible provided that it is relevant. According to the case of PP v Gan Ah Bee  2 MLJ 106, 108 (HC):
“It has long been held as a matter that the evidence obtained as result of an illegal or unlawful search does not affect its admissibility provided that the evidence so obtained is otherwise relevant to the case that is being heard. This proposition applies in general both civil and criminal cases.
Besides that, according to the case of Saminthan v PP  MLJ 39, held, the legality or illegality of a person’s arrest does not concern the court which is trying him and in respect of certain documents that were seized by the police during the illegal search of the appellant’s room, that the court was only concerned with the relevance of the document seized and not with the manner in which the police obtained possession of them.
In addition, the court is also not concerned with when such evidence was obtained. In the case of Ng Yin Kwok v PP  3 MLJ provided that the court should only be concerned with evidence to see if they are admissible, not when or how such evidence was obtained.
AN ADDITIONAL INFORMATION: in Islam ITS totally prohibited when the evidence obtained illegally...