This is the latest summary I received from the DVSA this morning after I provided additional information to my original complaint.
It is probable all types and makes of vehicles will, at some time, experience a mechanical or electrical component failure. These, by their nature can be unpredictable as can the site/location where it may occur. Therefore, DVSA considers the immediate impact any safety related issue may have on the vehicle in to determine if it is a safety defect as defined by the Code.
Our understanding is the vehicle has two-stage warnings, both of which are visual and acoustic, and the vehicle fully meets type approval requirements.
Initially the 12V supply should support secondary systems (including lighting and steering) allowing the vehicle to carry forward, slow down and be brought to a halt. Lighting, inc. hazard lights etc., should be still active at time of incident and ‘emergency call’ available. However, as with any vehicle, (ICE, Hybrid etc) if charging has been interrupted the battery will deplete over time, and, depending on usage, certain systems may not fully function.