548. Assistance by defendant: reduction in sentence and review of sentence.

If a defendant:

  1.  

    (1)     following a plea of guilty is either convicted of an offence in proceedings in the Crown Court or is committed to the Crown Court for sentence1; and

  2.  

    (2)     has, pursuant to a written agreement made with a specified prosecutor2, assisted or offered to assist the investigator or prosecutor in relation to that or any other offence3,

then in determining what sentence4 to pass on the defendant the court may take into account the extent and nature of the assistance given or offered5.

If the Crown Court has passed a sentence on a person in respect of an