I've been doing a bit of digging Re Hazards while braking and found the following
The relevant legislation is, according to HC116, Is regulation 27 of the Road Vehicle Lighting Regulations (1989). That regulation is a list of restrictions on the use of certain lights. Para 5 bans the use of Hazard warning lights: -
Used other than–
(i)to warn persons using the road of a temporary obstruction when the vehicle is at rest; or
(ii)on a motorway or unrestricted dual-carriageway, to warn following drivers of a need to slow down due to a temporary obstruction ahead; or
(iii)in the case of a bus, to summon assistance for the driver or any person acting as a conductor or inspector on the vehicle
Referring to point ii above, it would appear from the way I'm looking at it, that the auto feature built in to modern cars, must have stemmed from this point, as for most drivers the most likely place to be carrying speed is on a motorway.
Anyone needing to slow down rapidly from 70Mph on a motorway in any lane due to a hazard in front, would warn anyone following you that there is a potential hazard ahead and to take action.
Don't want to start a debate on the thread, but I thought fellow SCN'ers would find it interesting (or not lol)