“If on a defendant’s trial before a judge and jury for an offence a) evidence of his bad character has been admitted under any of paragraphs (c)-(g) of section 101 (1), and b) the court is satisfied that any time after the close of the case for the prosecution that i) the evidence is contaminated, and ii) the contamination is such that, considering the importance of the evidence to the case against the defendant, his conviction of the offence would be unsafe the court must either direct the jury to acquit the defendant of the offence or, if it considers that there ought to be a re-trial, discharge the jury.”