My Peugeot 306 GT Premium is excellent with regards to comments above. With lighting set to auto and running in day light, then yes it’s just the DRL and no rear lights. However. If the light dims it will then switch on the headlights, along with Rear lights. This includes when it’s raining or what ever driving conditions dims the sensors react very quickly to those changes.
Most cars do all of that now Joss (although some don’t react as soon as they should in the daytime when visibility is poor), but it all relies on the headlight switch being left on the ‘auto’ setting. The problem is that many people don’t have the switch on the correct setting and in fact I find that when cars go into dealers for servicing they often send them back with the auto headlights switched off, presumably so that the lights aren’t on when in the workshop!