"As was pointed out in Warren & Beeley the amount of drugs is only one of the factors to which regard must be paid in the sentencing process. However generally speaking and by way of guidance, where a massive quantity of Class A drugs has been imported, a sentence significantly in excess of 20 years, after a trial, should, in our judgment, be reserved for exceptional cases where, for example, the amount of drugs involved is truly enormous or the defendant is to be sentenced for taking part in more than one such importation, or the defendant has a previous record for serious drug dealing, or the defendant is at the pinnacle of responsibility for the particular importation."