Why do the BBC refer to Islamic State as 'so called' Islamic State?

You're slow on the uptake. They've been doing this for almost a year. First they phased out ISIS on its own because dimwitted idiots started targeting businesses and bullying girls named after the goddess or upper reaches of the Thames. Then they added "so-called" or "self-styled" to IS because it pisses them off not to recognise them as a legitimate country. I'm all for pissing them off.

Beacuse DAESH are not a legitimate group, and are murder inspiring terrorists who should be hunted down in the streets and shot like the dogs they are.

As for the BBC its as close to ordinary as they get, if the BBC told me its raining, id wear my sunscreen.

It is so-called because they are not officially recognized a government or a legitimate organization, but a movement and a terrorist group that fancies itself a caliphate in waiting. Nobody wants to give these barbaric murderous monsters a name.

You need to be officially acknowledged to be a State(governments need to send a letter of recognition), they're not acknowledged by the International Community, so they are 'so called', it's a terror-group pretending to be a Country.

The, BBC News has been using the term, "self-styled Islamic State" so not to make Isis, Isil, IS or Daesh sound legitimate,

Because almost all Muslims don't consider what ISIS is doing to be acceptable in Islam.

Supposedly, so as not to offend the other "so called pious muslims".

Because they are dhimmi scum.