“(4) Where a court—

(a) is determining the sentence to be imposed on a person for an offence committed while he or she was on bail,

and

(b) is required by subsection (1) to impose two or more consecutive sentences,

then, the fact that the offence was committed while the person was on bail shall be treated for the purpose of determining the sentence as an aggravating factor and the court shall (except where the sentence for the previous offence is one of imprisonment for life or where the court considers that there are exceptional circumstances justifying its not doing so) impose a sentence that is greater than that which would have been imposed in the absence of such a factor.”.