Looks like it's time for a reminder that the complete report is available to download (and read) from the AAIB website:
https://assets.publishing.service.go...017_G-BXFI.pdf
"The [test pilot] explained the difficulty in detecting reduced thrust during the ‘up vertical’ part of the manoeuvre, and given the pilot’s focus on external cues, if it was not selected by him he was probably unaware of it."