Well there you go. They could have called him and didn't, and I still wonder why that was? In any case, its their mistake, and therefore not the prosecution's problem.
Another thing worth noting
https://www.theguardian.com/uk-news...ucy-letby-appeal-court-what-could-happen-next
Dr Shoo Lee, an academic who researched the phenomenon of air embolus in babies in 1989, gave evidence to the appeal court on behalf of the defence, telling judges that the “only sign” of it was pink blood vessels “superimposed” on a pink or blue body.
When questioned by the prosecution, Lee accepted he had not assessed any of the victims’ medical records in Letby’s case or seen any of the witness testimony provided by other medical staff, who noted strange rashes on a number of the dead babies.
Oops! Why not? Why didn't the defense get him to asses the autopsy reports and the babies' medical records, or transcripts of the witness testimony.
I'm not sure if the UK has an equivalent of the US'
"Ineffective Assistance of Counsel" provision, but if they do, Letby should argue that. The defense didn't call a key witness or enter his research as evidence at trial, and didn't arrange for their key witness at the appeal to examine any of the important evidence or witness testimony. Smells like incompetence to me!