I hadn't even got as far as thinking about tapes as there's simply no evidence he had an AM pre murders. If he did AE would have considered such when she was working out how long it would take JB to reach the phone and then questioned either why AM wasn't switched on or how JB got to it before it kicked in.
The prosecution at trial would put it to the jury in terms of a) the AM was switched off or b) he was able to wake and get downstairs to answer phone before it kicked in. JB would have been cross examined on it. If he had an AM pre murders it would be highly relevant to his claim of a phone call from NB when he claimed he was sleeping "like a log" until he was woken up at circa 3.30am.
Bamber himself says he had an AM.
No point the prosecution asking him how he got to the phone in time. He will just say he always switched it off when he got home. Which they can't disprove.
They may have mentioned his AM in the narrative that he phoned GH from WHF.
Agree him having an AM is very incriminating. So you will always fight it.
How's the internal screws in Nevill's back & scolding hot rifle going?