You can find the answer on AAIB report admissibility
here. The case was Rogers v Hoyle - to cut a long story short, the AAIB reports are considered to be expert and may be used. (And was on this occasion too.)
The coroner has been making noises about the inquest, and many people are expecting a whole new 'investigation'. They may be disappointed. To quote the Lord Chief Justice when he ruled in 2016 on the Norfolk Coroner's demand for access to the CVR/FDR for an AW139 accident:
In the absence of credible evidence that the investigation into an accident is incomplete, flawed or deficient, a Coroner conducting an inquest into a death which occurred in an aircraft accident, should not consider it necessary to investigate again the matters covered or to be covered by the independent investigation of the AAIB. [
] [T]he findings and conclusions should not be reopened.
I think it will be hard for anyone to suggest that the AAIB report in this case is incomplete, flawed or deficient.