R v C [2007] EWCA Crim 2859, [2008] All ER (D) 19 (Apr)
The Court of Appeal noted that every summing up, particularly one delivered extempore, could, with hindsight, be rewritten or have other features incorporated into it.
However, that is nowhere near sufficient to demonstrate that a conviction is unsafe. A summing up is an individual creation, in which virtually everyone who hears it who is a party to a case on either side will find something that he would prefer to be expressed differently.
However, it is important to bear in mind that a summing up is not written for the Court of Appeal, which has not heard the evidence, but rather it is written for the jury who have been listening to the evidence. It is written for those who know, in particular, what is not disputed.