The parity principle does not operate where a co-offender has been granted immunity from prosecution, because the principle requires comparison of curial punishments and there are insuperable practical difficulties in comparing a court-imposed sentence with the position of an offender granted immunity by the Executive. Where a conviction appeal alters the factual basis upon which a sentence was imposed (here, removing the weapons element from a conspiracy), the changed basis impacts the assessment of objective seriousness and may render the original sentence manifestly excessive.
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