“If the information given is accurate, particularised, useful in practice, and hitherto unknown to the authorities, enabling serious criminal activity to be stopped and serious criminals brought to book, the discount may be substantial….Where, by supplying valuable information to the authorities, a defendant exposes himself or his family to personal jeopardy, it will ordinarily be recognised in the sentenced passed. For all these purposes, account will be taken of help given and reasonably expected to be given in the future.”