It’s for nobody in particular, Fred. Section 36, Youth Justice and Criminal Evidence Act 1999:
http://www.legislation.gov.uk/ukpga/1999/23/notes/division/4/2/2
“…gives courts the power to prohibit unrepresented defendants from cross-examining witnesses in cases where a mandatory ban does not apply under sections 34 and 35 [which cover some particular offences], but where the court is satisfied that the circumstances of the witness and the case merit a prohibition, and that it would not be contrary to the interests of justice.”
Very commonly used in Domestic Violence cases and quite often used when the witness, especially if a victim, is a young person.