I'm sorry mike but this is absolute cobblers. Where is there any evidence whatsoever of a "change of voltage on the line at 3.42"?
Don't be sorry, Vidvic, it's standard knowledge that the GPO used to test phone lines using voltage readings, and that by adopting this approach they could detect faults, or if the phone was off the hook, or not - this was how the GPO knew that someone had left the phone off the hook by 3.42am, after the handset had previously been resting in its cradle when the panic button was activated at 3.29am, it all boiled down to voltage when the line was tested, the voltage being different in the line when the panic button was activated with the handset resting in its cradle, as opposed to a reduction in the voltage when the line was checked by the GPO at 3.42am, phone off the hook...
There is no need to apologize, you obviously were not aware of the equipment and technology available to the GPO to test phone connections and telephone lines, as was the case in this instance