per ft.com: https://archive.fo/BIOej

    [The Derbyshire Police] declined to give more detail
    about what the evidential material consisted of.
 
    The term [evidential material] can be used to
    describe witness statements.

I don't know if it's still the case in the UK, but in the common law and still in the US this why all substantive evidence, with very rare exception (e.g. dying statements), is witness testimony given on the stand. It may seem absurd when a witness or expert is given a transcript of an earlier statement or report just to recite it, but this is exactly why.

The loophole is all the powers the police and government have to more-or-less punish someone before a trial, or even before charges.