It is illegal and when you get pulled and you can not turn them off your car may be prohibited. Fog lights are for foggy weather and not to dazzle others when it is raining and reflecting up from the wet road.....The clue is in the name. 
Getting pulled is unlikely (Policing done by speed and red light cameras these days) , it is getting harder to differentiate someone who is being a tool with their fogs on in clear conditions and someone who just has DRLs on.
I think DRLs are pointless personally, they don't make a shiny red, white, blue, green or black car any more visible in fair conditions, they do make motorbikes less noticeable as motorbikes though, now everyone has lights on.