I start from the approach that there is no sentencing tariff as such. Apart from the maximum sentence prescribed by Parliament, the intuitive synthesis approach to sentencing implies an absence of necessary relationship between one case and another. Accordingly, as the law stands, any notion of a mathematical norm above or below which a case might be cast according to aggravating increments and mitigating decrements is precluded by a general prohibition on the use of two part sentencing processes. At the same time, it is of the nature of sexual offences that some instances of an offence are more serious than others. Since that is so, there is a need for at least some degree of comparison. The requirement to have regard to "current sentencing practices" is properly to be understood in that context and the notions of manifest excessiveness and manifest inadequacy are similarly informed.
Secondly, the need to have regard to current sentencing practices does not mean that the measures of manifest excessiveness and manifest inadequacy are capped and collared by the highest and lowest sentences for similar offences hitherto imposed. In fact, as in theory, each case is different and so it is always possible that a sentence may properly rise above or fall below the greatest and lowest sentences previously imposed. At the same time, however, the nature of criminal conduct is such that there is not infrequently sufficient similarity between two cases to imply that sentences should be comparable and, if they are not, that something has gone awry.
Thirdly, and importantly, it should not be thought that the statutory requirement to have regard to current sentencing practices forecloses the possibility of an increase or decrease in the level of sentences for particular kinds of offences. Over time, views may change about the length of sentence which should be imposed in particular cases and, when that occurs, the notions of manifest excessiveness and manifest inadequacy will be affected. Accordingly, to say of an individual sentence of six years, or a total effective sentence of 15 years, that it is near as large as any before imposed for offending of this kind, is not necessarily an answer to the question of whether it is manifestly inadequate. One must allow for the possibility that sentences to this point have simply been too low. [83]