After section 274--
insert--
'(1) This section applies if, before the commencement of this section, a witness is given a notice in the prescribed form mentioned in section 123(1) in relation to the committal of a defendant.
'(2) The notice continues to have effect as if it were a summons to the witness issued out of the court that the witness was by the notice required to attend until--
(a) the proceeding in relation to the defendant is concluded; or
(b) the court otherwise directs; or
(c) 3 years after the commencement of this section;
whichever happens first.'.