Keith,
Google "BBC IS" .You'll find links to any amount of articles where the Beeb refers to IS without describing the terrorist group as "self styled" or "so called" .
As an example, see this Auntie Beeb article from 7 July, which refers to Islamic State, "IS" , "Isil" or "ISIS" eleven times , without once using a "so-called" or"self-styled" qualification:

The US-led coalition fighting the Islamic State group is "intensifying" its campaign in northern Syria, President Barack Obama says.
http://www.bbc.com/news/world-middle-east-33418021