“R. v. Clarke dealt with a particular kind of written statement, but in our experience the principle has always been applied, as it was in R. v. Adebanjo (1935) 2 W.A.C.A. 315, to any written statement in the possession of the prosecution which was made by a witness called by the prosecution and relates to any matter on which the witness has given evidence. Such a statement is not evidence of the facts contained in it and the only use to which the defence can put it is to cross-examine the witness on it and then, if it is intended to impeach his credit, to put the statement in evidence for that sole purpose: Evidence Act, Section 198 and 209.”