Fascinating read. The last paragraph caught my eye ...
I am not at all convinced, as a matter of law, that the government has the power to grant, by bilateral treaty or otherwise, immunity from criminal prosecution to foreign nationals, plainly outside the provisions of the Vienna Convention. This should be tested by the courts.
Maybe time for SCOTUK to swing in to action again ? The Dunn family might have a better shot challenging the basis of the immunity itself, now this has emerged. Not that it will procure the suspect in any case. But it might put the fear of God into US employees here.
Incidentally, why did they "need" immunity ? What UK laws were/are they breaking ?