Observer1940
Thank you for your post. Sadly, I have to accept that the cause was most likely pilot error and that the lack of a discernible horizon contributed to the error. Very much like what happened to an early Tornado GR1 loss over the Irish Sea.
There seems to be no evidence for there being a runaway tailplane trim actuator. As you say the ac seems to have been in a left bank and very shallow descent and simply cartwheeled in.
MB