21. Accused person to be a competent witness.- Any person charged with an offence punishable under this Act, shall be a competent witness for the defence and may give evidence on oath in disproof of the charges made against him or any person charged together with him at the same trial:

Provided that-

(a) he shall not be called as a witness except at his own request;

(b) his failure to give evidence shall not be made the subject of any comment by the prosecution or give rise to any presumption against himself or any person charged together with him at the same trial;

(c) he shall not be asked, and if asked shall not be required to answer, any question tending to show that he has committed or been convicted of any offence other than the offence with which he is charged, or is of bad character, unless-

(i) the proof that he has committed or been convicted of such offence is admissible evidence to that he is guilty of the offence with which he is charged, or

(ii) he has personally or by his pleader asked any question of any witness for the prosecution with a view to establish his own good character, or has given evidence of his good character, or the nature or conduct of the defence is such as to involve imputations on the character of the prosecutor or of any witness for the prosecution, or

(iii) he has given evidence against any other person charged with the same offence.