“(i) the seriousness of the offence itself, on its own or with other offences associated with it in accordance with the provisions of s.143(1). This is always a matter for the judgment of the court. (ii) the defendant’s previous convictions (in accordance with s.143(2)). (iii) the level of danger to the public posed by the defendant and whether there is a reliable estimate of the length of time he will remain a danger. (iv) the available alternative sentences.”